The movie begins in a black-and-white sequence in the city of Prague, Czech Republic, where James Bond has tracked down an MI6 section chief, Dryden, who has been selling information to enemies for profit. They chat about what it takes to be a 00- agent (one of the requirements is making two confirmed kills) and Bond casually tells Dryden that his espionage contact, Fisher died, and "Not well." Intercut with the conversation are black and white scenes of Bond and Dryden's contact fighting in a men's room. Bond finally pushes the man's face into an overflowing sink and holds him there until he drowns.
Dryden points a gun at Bond. "Shame. We barely got to know each other." He pulls the trigger, but James has removed the ammunition from the weapon. "I know where you keep your gun. I suppose that's something." Dryden continues to taunt Bond, asking him if he felt any remorse or guilt over killing Fisher. Bond remains passive, his face expressionless. Dryden says that Bond "needn't worry, the second is--" at which point Bond kills Dryden, before Dryden had a chance to say the word "easier". Bond puts his pistol away saying, "Yes, considerably." (Though not said explicitly, Bond found the killing of Dryden, his second such kill, "considerably" easier than the first.) In flashback, Fisher recovers from Bond's attempt to drown him and picks up his pistol. The frame instantly shifts to the series' iconic "gun barrel" sequence as Bond spins around and shoots the man. Blood runs down the frame, prompting the opening titles.
The scene shifts to Uganda where a group of freedom fighters is meeting with Le Chiffre, a private banker to terrorist groups around the world. The broker for the deal is a Mr. White, who invests their money and manipulates stocks so they get a 100% return on the investment. The terrorists, lead by a man named Steven Obanno, agree to allow the money to be taken for Le Chiffre's nefarious purposes. Once the deal goes through, Le Chiffre calls a stockbroker in London and has him short-sell a massive number of Skyfleet stocks, despite the broker warning him that he's betting against the market.
In Madagascar, Bond, on his first mission as a "00", is working with another agent, Carter, monitoring a terrorist, Mollaka, who is gambling on a match between a cobra and a mongoose. Bond's inexperienced partner agent is exposed after Mollaka gets a cell call and the terrorist bolts from the scene. Bond chases the man, who is an experienced "free runner" (parkour) who leads Bond through a construction site, onto several sky cranes and finally to the Nambutu embassy where he seeks asylum. Bond charges into the embassy, in direct contravention of international law and his orders, and catches Mollaka in the ambassador's office. Bond fights his way thru the halls of the embassy and finally finds himself surrounded by armed guards. The ambassador appears and orders Bond to let Mollaka go. Bond shoots the terrorist and a nearby gas tank and escapes in the explosion. He also steals the backpack Mollaka was carrying. Searching through the backpack, he finds a bomb and Mollaka's cell phone. Bond examines the bomber's messages briefly, seeing one with an American phone number and the word "ELLIPSIS." Bond keeps the phone.
Back at MI6, M is furious that 007's violent actions were caught on tape at the Nambutu embassy. Bond later breaks into M's home and hacks her top-level clearance so he can trace where the cell phone call originated from. When M enters she's startled and lectures him on proper protocol and conduct, stating she think it may have been a mistake to promote him to 00 status. Bond assures her that "the life expectancy of a 00 is brief, so your mistake will be short-lived." M tells him that "arrogance and self-awareness seldom go hand-in-hand" and she wanted him to take his ego out of the equation when on a mission. She also tells him to go on a brief vacation until she can decide how best to deal with him. Bond had discovered that the call to Mollaka originated at a posh beach resort in the Bahamas and so Bond goes there to investigate who made the call and why. He ends up finding a middle man, Dmitrios, who was working for Le Chiffre and that he was hired to find someone who could carry out a task for Le Chiffre. Bond meets Dmitrios and plays poker with him, winning his 1964 Aston Martin.
Bond uses the Aston to finagle a romantic evening with Dmitrios' spurned wife, Solange, to get information about her husband. She tells Bond that Dmitrios is going to Miami. Bond follows him there where he confronts Dmitrios, after seeing him put a bag away for someone to pick up later. Bond kills Dmitrios when he's held at knifepoint, however, the bag goes missing and Bond follows the man, Carlos, hired for Mollaka's job.
Bond follows Carlos to Miami International Airport, where he pulls a security uniform out of the bag and puts it on. He slips into the secured area of the airport and Bond follows him, having figured out "ellipsis" was the security code to get through the door. M calls Bond to tell him Le Chiffre will have Carlos destroy the prototype for a large airline named Skyfleet. The prototype is the largest passenger aircraft in the world and destroying it will bankrupt Skyfleet. Carlos sets off the emergency sprinkler system in the building to cause a diversion and slips out onto the tarmac. Carlos attaches an explosive charge to a refueling tanker after killing the driver (a cameo by director Martin Campbell) and starts driving it towards the plane. However, Bond manages to leap onto the tanker. The two have a vicious fight around the runways while being chased by the Miami-Dade Police. Eventually, Carlos leaps off the truck, and Bond is barely able to stop the tanker from hitting the plane. Carlos smiles as Bond is arrested and activates the charge. However, Bond has already discovered Carlos' small explosive device & attached it to Carlos' belt during the melee, and Carlos ends up killing himself.
Returning to Nassau, Bond discovers that Solange had been murdered and trussed up in a hammock. M explains she was tortured and killed by Le Chiffre because she was the only one left alive and he assumed she talked. Le Chiffre's plan was to "short-sell" hundreds of millions of dollars in Skyfleet stock and, in destroying their prototype, cause their stock to plummet and send them into bankruptcy so he could buy the shares back at cheaper value. Thanks to Bond, Le Chiffre has lost over $101 million. Now a marked man, Le Chiffre must find another way to earn the money back so his investors will not kill him. He sets up a high stakes poker match at Casino Royale in Montenegro for 10 players, with an entry fee at $10 million each plus a $5 million buy-back should they lose all their money. M informs Bond of the poker game and arranges to place Bond in the game as a replacement for a syndicate member, since he's the best poker player in MI6. M also has a homing device planted in Bond's left wrist so she can track him anywhere.
The British government will be putting up the money and, while Bond is on the train to Montenegro, he is met by Vesper Lynd, a Treasury agent who has been sent to monitor Bond and give a go, no-go should he lose the money. They talk on the train about each other, Vesper commenting on his cold nature and Bond remarking on how Vesper is retentive. Upon arriving they pose as a married couple and meet Rene Mathis, their contact in Montenegro. Each poker player has their money in a Swiss bank in escrow while they play and each one has a password to keep the money secured. Vesper has the account number but only Bond knows the password.
On the first hand, Bond deliberately makes a misjudged call to figure out how Le Chiffre bluffs (his physical "tell" involves him placing his left hand near his wounded left eye), however Vesper is not at all impressed, thinking Bond is inept. After a lengthy round of hands, a break is called. Bond places a tracking device in Le Chiffre's asthma inhaler and takes Vesper back to their room.
Le Chiffre is called back to his room by his girlfriend, Valenka. However, he is confronted by Obanno and his henchman, demanding his money back. They threaten to cut off Valenka's arm, however, Le Chiffre doesn't acquiesce. Out in the hallway, Bond hears Valenka screaming. He quickly grabs Vesper and they kiss in the stairway entrance to cover themselves. Obanno's henchman notices Bond's earpiece and attacks them both. The fight takes them into the stairwell, where the henchman gets thrown off the stairwell to his death, and James and Obanno have a knock-down drag-out fight all the way down the stairwell, Obanno wielding a machete. Finally landing on the bottom, Bond gets Obanno into a choke hold. Obanno tries to reach for Bond's pistol, but Vesper smashes it out of his hands. Bond finally kills off Obanno and orders Vesper to contact Mathis, who sets up one of Le Chiffre's associates to take the fall for the dead bodies by placing them in the man's car trunk. Bond finishes the poker session, but he returns to the room to find Vesper shaking uncontrollably in the shower from the fight. He holds on to her and comforts her.
The next day, during the continuing poker game, Bond loses all his money to Le Chiffre after misreading a bluff and admits to Vesper that he made a mistake. Vesper won't give him the buy back money saying he's going to lose it. Furious, Bond goes after Le Chiffre but is stopped by one of the other poker players, Felix Leiter, the CIA's representative sent to the poker match to catch Le Chiffre for the same reasons MI6 has sent Bond. Leiter tells 007 that he's doing poorly himself in the game and that he'll back Bond to re-enter the game; Leiter believes that Bond can beat Le Chiffre. In return, Bond will give Le Chiffre to the CIA.
Bond slowly builds his bank again and once again becomes a threat to Le Chiffre. Le Chiffre has Valenka poison Bond's martini with digitalis, causing Bond to suffer severe tachycardia. Bond goes to his car distressed and, communicating with medical specialists at MI6 headquarters, is about to use the defibrillator when he sees the the connection isn't plugged in and passes out. Vesper arrives, fixes the defibrillator kit and shocks him back to life. Bond, shaken, returns to the game. The final hand of the game is down to four players, including Bond and Le Chiffre, who go "all in", betting their remaining money, driving the "pot" well over $120 million. One man has a flush, while another has a full house. Le Chiffre has a higher full house and is about to take the entire pot when Bond reveals he has a straight flush and wins the game.
Bond has dinner with Vesper, who receives a call from Mathis stating that Le Chiffre has been apprehended by the CIA. Vesper leaves the dining room; seconds later, Bond realizes she's in danger. Vesper is kidnapped by Le Chiffre. Bond races after them in his Aston Martin, but has to swerve violently when he sees Vesper lying bound in the road. The car rolls several times, destroying it and injuring Bond, rendering him unconscious. Le Chiffre and his cronies take him, removing his homing implant. As Bond fades from consciousness, Le Chiffre tells him that Mathis was allied with his enemy.
Bond and Vesper are taken to a nearby tramp steamer and separated. Bond is stripped and bound to a chair with the seat removed, leaving his testicles exposed. Le Chiffre uses a large knotted rope, striking Bond's scrotum, demanding the password for the account the winnings have been secured in. Bond refuses, despite Le Chiffre's threats to kill him and Vesper. Through the pain inflicted on him, Bond tells Le Chiffre that his investors, who are already hunting him, will find him and kill him. Le Chiffre counters, saying that even if he murders Bond and Vesper, that MI:6 will still welcome him because of the knowledge he possesses about his terrorist clients. Le Chiffre finally draws a knife and is about to castrate Bond when gunshots are heard outside. The door opens and Mr. White, the broker who introduced Obanno to Le Chiffre, walks in, pointing a silenced pistol directly at Le Chiffre. Le Chiffre, suddenly frightened, pleads with him, saying he'll secure the money, to which White replies, "Money isn't as important to our organization as knowing who to trust." White then fatally shoots Le Chiffre in the forehead.
Bond wakes up in a hospital bed during a haze while he recovers. He talks to Mathis, whom he believes was responsible for his and Vesper's capture by Le Chiffre. MI6 agents appear, taze Mathis and drag him away.
Vesper visits Bond and they confess their love for each other. The Swiss banker in charge of the winnings account visits and Bond gives Vesper the password to key in; the password is her own first name. Bond resigns from the service to go away with Vesper, and they sail to Venice, Italy where Vesper says she'll get the money and Bond will get the supplies for the trip. When M phones 007 about his resignation, she says that they'll discuss that later but they need to talk about the money being returned to the British government first, which tips off 007 that Vesper was using him all along.
007 follows Vesper to a secret meeting where she turns the money over, in cash, to a man named Gettler. Gettler and a few of his men retreat to a building being renovated and a gunfight ensues. Bond shoots and ruptures the flotation bags that hold the building above water-level and kills the men. He tries to save Vesper, locked in an old elevator, but is unable to after she commits suicide by drowning herself. Bond recovers her body and takes her above water but is unable to revive her. Mr. White, who'd been watching the scene, is seen leaving with the suitcase full of money.
Sitting on the sailboat he and Vesper had been vacationing on, Bond talks to M, who informs him that Vesper had a boyfriend who was being held by Le Chiffre's organization. She had intended to pay off Le Chiffre's associates with the money to secure her boyfriend's release. M believes that there are no further leads, that the "trail has gone cold." Bond examines Vesper's cell phone and finds the phone number of Mr. White, which he theorizes she left for him purposely.
At Lake Como in Northern Italy, White arrives at a palatial estate. After he exits his car, he receives a phone call from someone telling him they "need to talk." Asking who the caller is, White is suddenly shot in the leg by a sniper. He falls to the ground and crawls toward the house. As he tries to climb the stairs and the familiar Bond theme music begins to play, Bond appears carrying a cell phone and a silenced HK rifle. As White looks up defiantly, Bond says "The name's Bond. James Bond." The closing titles roll immediately.