Why is Professor Childermass acting so strange?  Johnny Dixon and his friend Fergie decide to sneak  over to the professor's house to investigate. What  they find is wilder than anything they could have  imagined, for the professor leads them through a  secret cellar door and onto a rickety old trolley.  It's a time machine to yesterdays, and soon Johnny  and Fergie are off on the ride of their lives: to  Constantinople during the Turkish invasion of  1453! As the Byzantine Empire  prepares for battle, the professor decides to try to save  the people hiding in the Church of the Holy  Wisdom. But Johnny and Fergie. Desperate to stop him,  have hitched a ride, recklessly unaware that they  risk their lives--and risk being lost in the past...forever!