Danny and Dixie Fortune are two twins whose father has mysteriously disappeared. Their mother is grief-stricken, their younger brother sick, and the family is really poor. Danny then decides to go to his great-uncles for help. The twin uncles Mordecai and Zecharias are thought to be really strange and weird(which is sort of true...) and they are also rather mean. The inventor Zecharias had made a time machine and Mordecai, a historian, prods Danny to go into the past to find out a bit about history for him. If he does, then the they would give Danny and his family a check for ten thousand dollars! Danny is shocked and indignant that they were trying to use him as a guinea pig and leaves the house with his uncles' words still ringing in his head.
He tells Dixie about it and they reluctantly decide to go into the past, for after all, how could they let their younger brother die? They are given a "Recall Unit" which they need to come back to their own time or else they would be stranded in the past.
They are brought back into the time when the Pilgrims are just about to enter the Mayflower. Danny and Dixie goes aboard with them and are the Strangers along with many other people. But, (oh no!) the very next day, Danny discovers that the Recall Unit was stolen from him that night! He and Dixie are horrified, for they were now stranded in the past until they can find it. Determined to find the thief and the Recall Unit, they stay on the Mayflower.
What will happen to them if they can't find the Unit? Who had taken it?