Though Lincoln and his Plum Street friends need a clubhouse, the city plans to tear down the firehouse, which is simply old but not ""historical"" enough to be saved. . . . Mrs. Crauch says the place was once an opera house where people saw ghosts and an actor they called ""friend"" was taken away by the police in the middle of Julius Caesar. . . . Addled old Mrs. Patch says it was once a railroad but there are no tracks nearby. . . . Then when the club is holding its nighttime initiation there Lincoln finds notes about shipping bales to Canada and later, hiding from the police who come to investigate the racket, he discovers a secret tunnel behind the dressing room. . . . And so the old firehouse turns out to be historical after ali and Lincoln, who makes the underground railroad connection at breakfast, ""was jumping up and down like a yo-yo"" over the solution of another well-made, undemanding puzzle.