The phone number Adam dials to try to reach Amy was actually Robert Cormier's phone number in real life. A lot of fans and curious young readers called him, but he never once received a prank call (source).
Robert Cormier played Amy Hertz's dad in the movie version of I Am the Cheese (source).
Adam's hometown of Monument, Massachusetts, is based on the town where Robert Cormier lived nearly his entire life: Leominster, Massachusetts (source).
Cormier wrote the bike ride scenes of the book first and inserted the conversations between Brint and Adam later (source). Pretty neat how the writing process works...