Timequest explores the science fiction theme of altering the present day by traveling back in time and tampering with past events – specifically, preventing the assassination of John F. Kennedy.

On the morning of November 22, 1963, an elderly man who wears spacesuit-type clothing materializes in the hotel suite occupied by Jackie Kennedy.

The Time Traveler shows Jackie future television footage of the assassination and funeral of John F. Kennedy.

Kennedy, in a speech televised from a rally at Rice Stadium, recommits to the importance of the Apollo Program, but also expands it to be a project for all humanity, and openly calls for the Soviet Union to participate in it, appealing to Nikita Khrushchev to negotiate an end to the Cold War.

In 1979, a then sixteen-year-old Mead commits a burglary, is arrested and put on a prison bus; his fingerprinting enables now-President Bobby Kennedy to know the Time Traveler's name.

The film ends with Mead's younger self (rather than the older Time Traveler) dancing with Jackie in 1963 as a dream sequence, then shows the real Mead as a toddler in 1964 staring at televised footage of Jackie with her new baby, James, being discharged from Dallas' Parkland Memorial Hospital, where JFK had died in the original timeline.