Like any child his age, Brian is very hurt by his parent's decision to divorce and is having a difficult time coping. When the story opens, Brian is on his way to visit his father in Canada. Brian realizes that this is the first of many school vacations and holidays that he will spend being shuffled back and forth between his parents.
Brian's struggle is compounded by his knowledge of his mother's infidelity. One day while out playing with a friend, Brian spies his mother kissing a man in the parking lot of a mall. We can assume that this man is his mother's lover and quite possibly the reason his parents are getting divorced.
Brian refers to his mother's infidelity as "the secret" and he thinks of it often. It consumes his thoughts and sometimes his dreams. "The secret" causes tension between Brian and his mother. Perhaps he blames her for the divorce?