It Happened on a Train — Mac Barnett

Retired private detective and current seventh grader Steve Brixton has a new job: he takes out the trash for five bucks a week.

But it's hard to leave the old game behind.

On a train trip down the California coast, Steve and his best chum, Dana, are pulled into a mystery involving a fleet of stolen automobiles, a vanishing girl, and a phantom train car.

For a great detective, the best part of retiring is coming out of retirement.