Tread Perilously celebrates its 400th podcast with the final episode of Supertrain -- "Where Have You Been Billy Boy."

When the FBI arranges for a fugitive transfer aboard Supertrain, Randall gets anxious. But will it matter to an aggressive magazine writer, a pregnant woman, a newlywed couple, and an old man when the fugitive -- who continues to maintain his innocence -- accidentally takes them hostage in the dining car? Will Randall be able to handle the situation? Will Flood make things worse? And will a small town sheriff turn Supertrain into a passenger liner of blood? Meanwhile, Penny gets accosted by a traveler.

Erik momentarily forgets Skipjack. Justin hears the laugh track for the first time ... again! The sound editors who added the canned laughter finally get memorialized with a sketch. Penny is chosen as Supertrain's series MVP. Justin recalls the train is nuclear powered and supersonic. A discussion about airplane disaster movies breaks out. The pair also stump for Carnival of Souls. Justin finds a new role for Weird Baby Man. Surprising guest stars lead to many potential future podcasts. Rue McClanahan makes a surprising appearance. A final analysis of Supertrain is made and the ghost of Bob Crane haunts the proceedings.