The Pearl

After effectively proving physical time travel cannot possibly exist, Professor David Melville goes to bed one evening and wakes up in his childhood bedroom, surrounded by familiar things.

So far, his quiet life has been dominated by a secret he has kept hidden for the past thirty-five years. But he's about to embark on a journey where he will see and do things he never dreamed would be possible in his lifetime, one of which is running up a flight of stairs without dying from a heart attack.

Abducted by aliens (although they consider this a mere technicality), he is shown technology that in the wrong hands could spell disaster for humanity. Unfortunately, they have lost control of it and need David to retrieve it for them.

One of the aliens thinks David is the right man for the job, the other one thinks he's an idiot...