It’s Christmas Eve, and the opening night of “A Midsummer Night’s Dream” in a student production at the reconstructed Globe Theatre on London’s South Bank, and 16-year-old Charlie has the coveted role of Puck. 

The director wants Charlie to exit through the trap door in the stage, “the way they did it in Shakespeare’s day.” But Charlie’s drops are awkward, and he remains behind to practice while the rest of the cast and crew break for dinner. 

When a mysterious man in the back of the theatre causes Charlie to flub a line, he drops through the trap door, and is taken back to 1594 and the original premiere of “A Midsummer Night’s Dream.” 
After Charlie learns the “secret” that allows him to travel back and forth through the trap door, he settles in for several weeks after he gets to see a copy of Shakespeare’s lost play, "Cardenio." 

Charlie’s dad is a renowned Shakespearean scholar who’s spent his entire life searching for the lost "Cardenio." And Charlie’s determined to remain in 1594 until he can secure a copy to take home with him. 

Charlie becomes a member of the Globe acting company and while trying to get a copy of "Cardenio," he gets caught up in a plot to assassinate the Protestant Queen Elizabeth I and install the Catholic Mary Queen of Scots in her place. Charlie provides information to Elizabeth’s spy chief, Sir Francis Walsingham, by showing him how Mary sends messages to her supporters: in a waterproof stopper in a weekly barrel of beer supplied to Mortonsfield Castle, where Mary has been confined under house arrest for many years. 
When Charlie realizes the manuscript of "Cardenio" will not travel with him back to the future, he must find a place in the London of 1594 where he can hide the invaluable manuscript so he can retrieve it 400 years later when he finally makes it back home. 

And—a mysterious man tells him if he doesn’t return to his own time by a certain date, he’ll remain in 1594 forever.