प्लॉट

A surprise leap forward in time strands Enoch in 1931 and lands the team in another unfamiliar decade; in order to stop the chronicoms from launching their future-dismantling plan, the agents must infiltrate one of S.H.I.E.L.D.'s most secure bases.

The SHIELD agents are pulled through the time threshold to 1955, where they try to stop a Chronicom plan to destroy Area 51 - and the SHIELD brain trust assembled there. Coulson and Jemma go in posing as a pair of SHIELD agents, including Peggy Carter. However, the base director, Daniel Sousa, quickly sees through their ruse and has them arrested.—Gislef

A young couple, Barb and Biff, park out in the desert near Groom Lake, Nevada, and lie in the back of Biff's truck while looking up at the stars. When Barb complains that she's cold, Biff gives her his jacket and says that he saw a flying saucer in the sky a few nights previously. Barb thought that his claim was just a line to get her up there, and as they kiss static distorts the truck radio. The Zephyr appears overhead in a flash of light, and lands nearby. Barb screams in terror as the Zephyr flies past them overhead.

In the Zephyr, the SHIELD team run to the controls and confirm that the autopilot activated the engines and brought them down safely. The Zephyr lands and its cloak engages, and the team realize that Enoch didn't get aboard in time, and is stranded in 1931. Simmons picks up a hand radio and picks up a local radio station broadcasting Perry Como, and they realize that they're in 1955. Coulson checks the topographical map and confirms that they're near Groom Lake: the home of Area 51.

Luke meets with his Chronicom superior, Sibyl, and reports that their adversaries appear to be following their time trials. Sibyl notes that she said it might be a possibility, and Luke's underling notes that they could have eliminated the SHIELD agents when they had the chance. He asks why they're set to self-destruct when compromised, and Sibyl notes that it would scatter future technology in the past and hasten the formation of SHIELD. She says that they must be delicate with time, and Luke asks if Helius is still a viable plan. Sibyl says that she's calculated every outcome and if done properly, it will work and be brutal.

The next morning, Simmons tells the other that they haven't completed their mission yet. Daisy notes that she made the decision on her own to have Deke kill Freddy, and Mack reminds her that doing so would accomplish the Chronicoms' goals for them. He tells Deke to follow his orders until the mission is done, and Yo-Yo wonders how they'll know when the mission is done. Simmons explains that they're drifting through time in the Chronicoms' wake, and she doesn't know how many more jumps they will make.

Mack says that they need to find the Chronicoms' ship and go on the offensive, and Coulson reports that they know Area 51 is a SHIELD base because all of the Area are. According to the archives, there was a classified SHIELD project at Area 51 in 1955 called Helius, and it could be what the Chronicoms are after. Simmons remembers that Helius was an early attempt at an ion fusion reactor, but was never fully realized and the tech was mothballed. Deke is aware of the technology being used for ship-killer energy beams in his time, and they figure the Chronicoms wants the reactor so they can destroy the Zephyr.

Later the team goes to a nearby diner. Mack and Yo-Yo and sit in a booth together. He admires her new robotic arms, and she tells Mack that her superpower isn't working. Mack figures that she's still recovering from the Shrike infection, and tells her that it's time for her to lose patience.

Coulson and Daisy sit together and discuss how Melinda didn't seem to be herself because she didn't react to the LMD Coulson.

The man the team is waiting for, Gerald Sharpe, comes in. Sharpe is with Department of Defense, and he gets some coffee. When he asks for cream, Daisy drugs a container and offers it to Sharpe. When Sharpe passes out, the team take him to a tented over area within the Zephyr and they figure that since he's just a bureaucrat, they should be able to crack him when he wakes up. Melinda comes in and calmly asks what year they're in. Mack tells her when and where they are and what their mission is, and Melinda asks when they go in. The team explains that Coulson and Simmons are heading there, and Coulson took Sharpe's ID papers.

Coulson sand Simmons drive to the gate of Area 51 and get in using Sharpe's papers. They go in and the officer who greets them, Lt. Carpenter, points out that Simmons isn't on the visitors list, and Simmons flashes a fake SHIELD ID identifying her as Peggy Carter.

A scientist, Dr. Pascal Vega, shows Coulson and Jemma around the major lab and shows off their "new" communicator watch. Vega shows them an electromagnetic pulse discharger that the scientists there have developed, and Jemma mutters to Coulson that she could save them decades of effort. The scientist then shows them a model of Helius, while the real one is on the testing field. He confirms that a science team comes in daily and Coulson says that they have to interview each of them. Vega asks if it's about the test that afternoon, and Jemma says that it is even though she has no idea what test he's talking about.

Deke and Daisy are in the Zephyr, and monitor things thorough the hidden camera in Coulson's fake glasses. Meanwhile, Mack and Yo-Yo question Sharpe to find out who he has given access to Helius. Sharpe tells them that he won't tell them anything because he's a loyal American, and figures the agents are Commies. When Sharpe calls Mack "boy", Mack takes offense and Sharpe boasts that he wrote the field manual on soldiers resisting interrogation.

Coulson and Jemma question the science team, and Jemma warns that any scientist could be mistaken for a Chronicom. Coulson says that all they have to do is trigger an emotional response to determine if they're human or Chronicom, They question the scientists and provoke emotional responses by asking them how they feel about actors and movies, and words like "moist".

Vega tells them that new MPs have come in, and Coulson goes to question them. Meanwhile, a SHIELD agent arrives and Carpenter tells him that Peggy Carter is there. The agent, Daniel Sousa, is surprised to hear that Peggy is there and goes to see his former partner.

Deke and Jemma go over files, and Deke points out that things are messy between her and Mack. He tells her not to put it on him to commit murder, and Daisy says that agents have to take orders. Deke points out that she's not his commander, and Daisy notes that she outranks him. She says that Hydra is infiltrating the government, and one death could have saved countless lives. When Daisy points out that Deke didn't use to hesitate about killing people, Deke says that he's not the guy she first met and he doesn't want to be that guy. Daisy says that she knows, and then notices a file on Daniel. It says that he's Peggy's old partner.

Daniel goes to the lab and finds Jemma questioning a scientist. He immediately realizes that she's not Peggy and when Jemma claims that she is, Daniel feigns nor knowing her. Daniel talks to her privately and Jemma says that they believe the base has been infiltrated. He says that he's in charge of the SSR office in LA, and Jemma realizes who he is and she isn't fooled by her ruse. Daniel draws his gun and Jemma figures that he'll be arresting her.

On the bus, Coulson questions the newcomers, trying to provoke emotional responses. Daniel comes on the bus and orders Coulson's arrest, and Coulson recognizes Daniel and says that he's a big fan. He sends a photo of Daniel to the Zephyr, and Deke runs facial recognition on the people that Coulson has seen. Mack knows them as SHIELD power players of the era. Melinda and Yo-Yo come in from interrogating Sharpe, and Melinda complains that Sharpe called her an "Oriental". Mack tells them that violence isn't an option and figures that Deke should talk to him since he's the only white male there. Deke points out that he has zero SHIELD training,, but realizes why they think he might have better luck and goes to question Sharpe.

Daniel tells Carpenter to keep Coulson and Jemma in holding, and bring him the visitor logs so he can find out how they got into a secure SHIELD base. He goes into his office and finds Daisy there. She says who she is is on a need-to-know basis and Daniel demands to see her credentials. Daisy gives him forged ID proving that she's with the CIA, and agrees that Daniel should call CIA HQ and confirm who she is but points out they might not be happy to learn two moles snuck in under Daniel's command. She knows all about Daniel's activities with the SSR, and Daniel asks if Daisy is there because of the report he sent to the CIA. He says that they have to root out sleeper agents within SHIELD, and Daisy assures him that he isn't crazy, and Coulson and Jemma might be the key to proving that he's not crazy. Daniel takes them to her.

Deke visits Sharpe, slow claps, and claims the entire thing was a test to determine if Sharpe would crack. Sharpe figures that Deke is the man in charge, and Deke asks if Helius is secure. Share doesn't believe Deke is who he claims, and says that Helius isn't functional and invites the supposed Communists that he thinks have captured him to take it. Deke leaves to tell the others, and Sharpe starts gnawing through his bonds.

Deke tells the others that Helius is a dud and figures that a Chronicom can power up the device and get it to work, as long as the Chronicom is willing to sacrifice himself. The resulting detonation will destroy everything in miles, taking out the entire brain trust of SHIELD. Mack figures they need to unleash Melinda, even though she currently has no emotions.

Vega demonstrates the wrist communicator, while a female Chronicom posing as a scientist secretly infiltrates the Helius controls.

Yo-Yo and Melinda infiltrate the base as pilots and Melinda says that she knows she should go easy on the civilian scientists. The two women put on flight masks, enter the main lab, and toss in gas grenades, figuring that the gas will only affect the humans but not the Chronicoms.

Daniel and Daisy go to Coulson and Jemma's cell, and orders them out. Daisy says that she'll need time with them alone, and Daniel refuses. An alarm goes off, and Coulson breaks his handcuffs and tosses the distracted Daniel in the cell.

In the main lab, Yo-Yo and Melinda find the Chronicom who isn't reacting to the gas. Melinda panics at the sight of the fleeing scientists and freezes up, and the Chronicom runs when she realizes that they knew what she is. Yo-Yo tries to superspeed after her but can't, and Melinda collapses to her knees saying that she can't breathe. She pulls off her mask to catch a breath and starts choking on the gas, and Yo-Yo goes to her and gets Melinda's mask back on her, then takes her out.

At the test site, Helius activates.

Yo-Yo and Melinda get out into the hall and Melinda says that she doesn't know what happened to her and it's never happened before. She doesn't want to talk about it, and asks Yo-Yo what happened to her. Yo-Yo says that she doesn't want to talk about it, and they go after the Chronicom.

On the Zephyr, Sharpe gets free and enters the control cabin as Mack and Deke try to shut down Helius by remote. Mack tells him to take it easy, and then punches Sharpe unconscious.

When the agents get outside, Vega is there with the other scientists. He tells them that someone started up Helius and they can't stop it. Coulson tells him to evacuate the other scientists and Vega goes. Melinda and Yo-Yo join their teammates, just as the Chronicom drives off in a jeep. The two women steal another jeep and go after the Chronicom,

The Chronicom smashes through a gate and drives to Helius, ignores the MPs' bullets, takes their rifles, and shoots them dead. She then attaches a Helius power cable to herself and powers up the reactor to cause it to explode. Melinda and Yo-Yo arrive and Melinda attacks the Chronicom. She fights back, and Yo-Yo goes to try and disconnect the Chronicom's cable from Helius.

Jemma, Daisy, and Coulson go to the main lab and Jemma tries to use Vega's pulse device to shut down Helius. A Chronicom posing as a scientist comes in and attacks them, and Coulson tackles him and shoves him out into the hallway.

The female Chronicom manages to shove Melinda back and pull Yo-Yo down just as she pulls the cable out of Helius.

Coulson and the male Chronicom continue fighting, evenly matched because of Coulson's LMD strength.

Melinda and Yo-Yo double-team the female Chronicom, and she wraps the cable around Yo-Yo's neck and then tries to plug it back in. It can't quite reach because it's wrapped around Yo-Yo's neck, and Melinda tries to free her teammate.

Coulson manages to pin the male Chronicom to the floor. Daniel arrives, draws his gun, and orders Coulson to get off the Chronicom. The Chronicom takes advantage of the distraction to pin Coulson, and slam his head into the floor. Daniel hits the Chronicom with his cane, and it finally grabs it and shoves Daniel back. It pins him to the wall, choking him.

The female Chronicom manages to plug the cable back in,

Jemma and Daisy rewire the pulse generator to expand its range. When Jemma activates it, it shorts out the Chronicom and Coulson, all of the lights, and the Chronicom at Helius. She falls, releasing the cable and freeing Yo-Yo. The female Chronicom self-destructs, melting down.

Daniel finds the self-destructed remains of the male Chronicom and recovers its fake ID badge from the remains. Carpenter and a MP arrive, and Daniel tells them that they need a medic for Coulson. He tells Carpenter to search the base for other infiltrators. As he walks off, a spark glows in the LMD Coulson's eye.

On the Zephyr, Deke and Mack take off after leaving the unconscious Sharpe outside in the desert. Sharpe wakes up and sees the Zephyr hovering over him. Mack speaks to him over the loudspeaker, calling Sharpe an Earthling and telling him not reveal that he was captured by "aliens", or they'll probe him the next time they abduct Sharpe. The Zephyr flies off and Sharpe goes to the diner and yells that he was abducted by aliens. No one there believes him as he rants about how the aliens were Communists from the future.