Brother detectives Frank and Joe go full-steam ahead to find the truth in the twenty-third book in the thrilling Hardy Boys Adventures series. The Hardys and some of their friends hop aboard an old train that’s been restored and turned into a murder mystery experience. A cast of actors will perform an immersive theatrical production while passengers dine in style, assume roles in the game, and ultimately try their hand at solving the case. This should be a cakewalk for Joe and Frank! The production is a mess. The actors are lousy, fumbling their lines and spelling out obvious clues. At least the food is pretty good. But just as the Hardy Boys are trying to make the most of a disappointing situation, one of the cast members goes missing. At first, the audience thinks that the show is taking a turn for the better, but it quickly becomes clear that this is not part of the act. For the Hardys, the mystery has gone from good fun to deadly serious. And trapped on a train full of people who aren’t who they say they are, everyone is a suspect. Will Frank and Joe be able to figure out how someone can vanish into thin air on a moving train before this case goes completely off the rails?

A sleek new hydrofoil is scheduled to start ferrying passengers between Bayport and Cape Cutlass. But business enemies of the hydrofoil owner have stirred up a hornets’ nest of violent opposition among small boat owners. Fearing sabotage, he begs Frank and Joe Hardy to guard the Flying Express on her maiden trip. Startling developments plunge the teenage detectives into a dangerous chase by sea, air, and land in pursuit of a gang of hardened criminals who operate by the signs of the Zodiac. Tension mounts when the Flying Express vanishes – and so does Sam Radley, Mr. Hardy’s skilled operative. Peril stalks Frank and Joe’s every moves as they hunt down the terrifying gangleader Zodiac Zig and his vicious henchmen.

After the new hydrofoil they are guarding is stolen, the Hardy boys face frequent danger in solving a mystery involving criminals who operate by signs of the zodiac.