Nick Miller has discovered the key to time-travel. Using a small plane located at his local airport in Vermont, the local college professor manages to fly 50 years into the future, and return to the present day (1991).
Hoping to capitalize on this discovery, Nick places two calls:
-the first call is to a local company called GenCorp, with Nick claiming he's developed a new fuel-efficient engine.
-the second call is to the local newspaper, where Nick claims his Grandmother is going to skydive for the first time.
The next day, Nick meets Matthew Paul from GenCorp, and Lisa Henson from the newspaper. Nick is surprised to see Lisa as they both went to school together long ago. After coaxing both of them into his airplane, Nick then tells them about his discovery of Time-Travel. Though Matthew is apprehensive, Lisa suggests they go 50 years in the future.
Nick manages to take them to 2041. After landing, he shows them all that has changed. Nick also claims that he wishes to obtain an R&D grant because of his discovery, as he is currently out of money. Matthew then explains that once they get back, he intends to tell the head of GenCorp about Nick's discovery as soon as possible.
Some time after the three have returned, Matthew makes good on his promise, and Nick shows his discovery to the head of GenCorp, J.K. Robertson. Robertson immediately wishes to do business with Nick, and also offers a position at GenCorp to Lisa. However, Lisa refuses and cautions Nick that associating with GenCorp is a bad idea. Nick tries to get her to reconsider, but she walks away.
After some time, Nick turns over the information he has regarding his time-travel experiments, but on trying to access the files that are being kept in GenCorp's computers, finds that he does not have access to this.
Going to the local supermarket, Nick comes across Lisa. Lisa apologizes for the way she reacted the last time they talked, but Nick claims he has a surprise for her. Taking her to the airport, Nick gets access to his plane, and takes Lisa back to the 50's on a date.
During their time jaunt, Nick then goes forward to 2041. However, the two find that the future now is in anarchy. When Nick mentions time-travel, one group takes him and Lisa in an attempt to get their 'Transport.' Nick and Lisa manage to escape back to the present. Nick then goes to GenCorp and explains to Robertson what he and Lisa saw. However, it soon becomes apparent that Robertson has had some hand in the changes to the future. He explains that he has already used Nick's technology to build his own time vehicle out of an airplane. Nick soon realizes that in signing over his discovery to GenCorp, they now have total control.
Robertson attempts to have Nick and Lisa turned over as 'Spies' to prevent them from telling of GenCorp's plans. However, the two manage to escape. Heading back to the airport, they manage to trick their way into getting Nick's plane out of the hands of GenCorp security.
Once airborne, Nick decides to leap back to the day when he gave the demonstration to Matthew and Lisa. Lisa does explain that while it will prevent GenCorp from knowing about Nick's discovery, it also will mean that she and Nick will not meet.
Nick still leaps back in time, but finds that Robertson and Matthew Paul are right behind them. Robertson fires on Nick's plane, wounding Lisa severely, and damaging the plane. Nick then bails from the plane as it crashes in a fireball. Nick manages to make it ashore, and heads towards the airport, hoping to stop his past-self from giving the time-travel demonstration.
Meanwhile, past-Lisa is diverted from meeting past-Nick about the 'skydiving Grandmother,' and told to investigate a plane crash. When she arrives on the scene, the forensics team mentions that a body in the wreck is so badly damaged, dental records will need to be investigated. Checking the number on the tail of the plane, Lisa finds it registered to Nick.
Past-Nick meanwhile, has given his time-travel demonstration to Matthew Paul, who is planning to bring Robertson to view the machine. After he leaves, Lisa arrives at the airport where she meets Nick and discusses what she found out. However, she's surprised to find that Nick claims to only own one plane, and it is sitting intact on the tarmac!
After they go back and check the wreckage, Nick claims they need to check on something, and he and Lisa take off in his plane (supposedly to time-jump somewhere, but this is not fully explained).
Meanwhile, the Nick that was on the plane that crashed has made it to the airport, only to find the plane gone, and runs into Robertson and Matthew. They also find Nick's mechanic Marty, and take both of them prisoner. Hoping to keep them from telling of what he has done (and is going to do), Robertson decides to time-jump them back to 1776, and kill them there, leaving the two as 'unaccounted war-dead' in the past revolutionary time period.
Back in the past, Nick and Lisa have returned, unsure just what to do now. Nick finds that Marty is missing, and Lisa calls the newspaper to check on the dental records...only to find that the body that was in the crash was her!
Back in 1776, Robertson tries to get Matthew to help him execute Nick and Marty, but when Matthew refuses, Robertson kills him. Just when it looks like Nick and Marty will be killed as well, past-Nick and past-Lisa appear, along with some revolutionaries. Robertson manages to scare them off, but as a nearby revolutionary battle happens, Robertson runs off on his own, leaving Nick to talk to his past self. Both of them come to an agreement to destroy the time-transport, with the present-Nick taking a horse and going after Robertson in his transport.
Nick and Robertson scuffle in the plane which causes it to crash. Nick attempts to emerge from the plane, but is accousted by Robertson. Robertson ends up killing Nick, but is killed himself when a section of the plane that is stuck in a tree falls on him.
Back in the altered past timeline, Matthew brings Robertson in from the city, but is surprised when Nick claims that Matthew wanted to introduce him to the star of the new GenCorp commercial, "Ms Gilda Hines, 80 years old and a world-class skydiver." Matthew tries to convince Robertson that Nick does have a time-transport, but finds that Nick's plane has none of the electronic equipment. Robertson then fires Matthew on the spot and leaves. As the CEO drives away, Nick comes up behind Matthew and says, "At least he didn't shoot you this time," leaving the pink-suited fellow perplexed.
In the closing moments of the film, we see Nick erase his data regarding the time-transport, and go to a local supermarket. While there, he encounters Lisa, and begins a conversation with her.