Ben leaps into an army colonel in an elevator with four others as they prepare to view a nuclear reactor. It’s 10am.

Mallory Yang turns on a recorder in her bag and begins to interview the lead scientist, Dr. Woolsey. He is a Nobel Prize-winning scientist in the field of sustainable nuclear energy.

This reactor will power a city with recycled nuclear fuel. As Ben figures this out and Woolsey explains it to Yang, the custodian Moe Murphy starts cleaning up a spilled soda.

Addison explains it’s September 12, 1962. The group is watching JFK give a speech about going to the moon and the future of technology. When Ben asks about the future of this reactor, Addison discovers it is going to be shut down this very day.

Eugene H. Wagner approaches Ben and tells a science joke.

Addison returns to HQ to get Jenn to dig into the records to see if there’s more info on the reactor near Fort Worth. She finds info on Dr. Woolsey. History has him dying on September 12, 1962 of a heart attack.

In the control room, Woolsey winds his watch. He makes a speech and instructs Wagner to initiate the reactor. Wagner has a problem with his pen. Ben lends him a pencil. Ben finds an envelope in his pocket, addressed to Colonel Parker.

Jenn discovers that Woolsey isn’t the only person in the room who dies around September 12. Yang is supposed to die in a car accident and Colonel Parker dies of an accidental weapons discharge. Wagner dies of an overdose. Murphy is killed in an electrical accident.

Jenn and Addison realize the deaths are a government cover up.

In the control room, the group counts down to the reactor start up. Addison rushes to get back into the imaging chamber.

The group applauds the successful start up but Ben notices a panel of flashing red lights, indicating dangerous levels of atmospheric radiation, gamma radiation, and problems in the lower axial zone and fission accumulator.

Woolsey asks why the reactor’s coolant is draining. Alarms start ringing. Addison yells for him to run but it’s too late and the group is engulfed in flames.

At HQ, Ben’s vitals flatline. Everyone is in shock and Addison falls to her knees screaming. Ian comforts her.

Suddenly, the monitors revive.

In 1962, Ben leaps into Wagner as he rides the elevator with the group before the demonstration.

At HQ, Ian tells the team they are dealing with a time loop. Addison insists that they let her back into the imaging chamber.

The group views the reactor (again). Addison arrives and she and Ben confront the fact he’d died. Addison tells him about the time loop and he realizes he needs to stop the reactor from exploding.

At HQ, Ian brings up the fact there’s an expert on time loops. Magic wants to talk to them. Ian tells him it’s Janis.

Janis is reluctant to help them but relents and agrees to help until Ben is out of the loop.

In the reactor, Ben tries to warn everybody. Woolsey is upset he is panicking and tries to downplay it to Yang, the reporter. Ben notices pages missing from Wagner’s ledger and starts recalculating the data. Woolsey is agitated, so Ben distracts the group with Kennedy’s speech.

Ben plans to drain the coolant and check the core.

Jenn tells Magic it’s weirdly coincidental that the moment Janis is in the building, Ben gets stuck in a time loop.

Ben and Addison examine the core and find a bomb. It detonates but doesn’t cause the reactor to blow. However, it causes a hydrogen gas leak which mixes with the oxygen in the air and ignites, killing Wagner, aka Ben.

Ben leaps into Mallory Yang.

Addison returns to HQ to find Janis in the room. Ian informs them Ziggy predicts the saboteur is one of the group in the elevator.

As the reporter, Ben asks Woolsey if there’s anyone who would want to see the reactor fail. Woolsey assures them they are in the safest facility in America.

Interviewing Colonel Parker, Ben learns he is concerned about Communist interference. Ben learns Wagner’s been on the project from the beginning. He’s been a fan of Woolsey since he was in high school.

Ben interviews Murphy about his interest in the project. Murphy tells him he loves science fiction.

Ben discovers Mallory recorded something before entering the facility. It turns out she is there to expose Woolsey as a fraud. As they realize this, the reactor blows up again.

At HQ, Addison confides in Magic that she feels like she’s grieving Ben even though he isn’t actually dying. In fact, she says it feels like her Ben died the night of the engagement party when he leaped.

Magic encourages her to hold onto the idea that Ben will come home. She asks if he’s doing the same with his hope to bring Sam home.

Ben leaps into Woolsey. He uses the opportunity to find out why Yang is actually there. She goes on the offensive accusing Woolsey of being bought off by the government. She warns him to stay away from her sister, that this endeavor is all on her.

At HQ, Ian and Janis talk about her dream to follow in Al’s footsteps and work at the Quantum Leap project. Ian points out that she and Addison are very similar people.

Ziggy narrows the suspects to Woolsey and Murphy. Janis asks to see the data. She realizes Ziggy’s determined that Ben can only leap into a body once which means the looping ends when he runs out of bodies.

Addison overhears this. She goes to inform Ben. The reactor explodes.

Ben leaps into Murphy. He leaves the mop behind in the elevator. He can’t get into the reactor because he isn’t Wagner anymore but he realizes he has keys to the offices. Security gets suspicious and calls Woolsey in the control room.

Woolsey demands security deal with it themselves. Hanging up the phone, he winds his watch and slips on the soda that Murphy didn’t clean up this time.

Ben and Addison search Woolsey’s office. Ben notes that this isn’t Groundhog Day, it’s Rashomon. Addison sees The Longest Day noted in Woolsey’s book for October 4. Addison hears someone and warns Ben.

He picks up a trash can to look like he’s cleaning and sees Colonel Parker walking past the door. He finds a torn up memo in the trash indicating the reactor is actually for making nuclear weapons.

Colonel Parker returns and pulls a gun on Ben when he hears him say blowing up the reactor is the better plan if it means saving thousands of lives from nuclear weapons.

The team debates whether to let Ben finish the leap or pull the plug on the project in hopes of saving his life. Janis insists they let him finish.

Parker asks Ben/Moe if he’s the one sending the letters. He pulls out the one Ben saw on his first leap. It’s an anonymous letter demanding Parker kill the project.

Ben realizes Wagner sent the letters based on the paper and the missing pages from his ledger Ben noticed earlier. Wagner tells Woolsey he found the memo from the military. He’s angry the reactor is going to be used to make weapons of mass destruction. Yang gets it all on her recording.

Wagner pulls out his pen. Ben realizes the pen click is the trigger. He talks Wagner down by pointing out that his sacrifice won’t stop the development of nuclear weapons but it will kill the people in the room.

Wagner hesitates and Parker shoots him in the arm, causing him to drop the pen. Ben catches the pen. As he’s taken away, Wagner points out that the wrong hands will always gain great technology and predicts it’ll destroy them all one day.

Addison fills Ben in on Murphy’s sci-fi book, Yang’s expose that turns the reactor into the power plant Woolsey and Wagner had intended it to be, but Ben’s not celebrating.

He wonders if the Quantum Leap project could be the next experimental nuclear reactor, falling into the wrong hands one day and being used to destroy rather than save.

Before he leaps, he tries to tell Addison Wagner’s joke.

Jenn checks in with Magic. She wonders why Magic sided with Janis on whether Ben should finish the leap or not. He says he sided with Janis today because he should’ve sided with her when she wanted to be part of the project and now they’re dealing with that fallout.

Janis approaches Addison and offers an olive branch – the name of the person who told Ben to leap in the first place.