In the first Robby Hoenig adventure, Secret Under the Sea, an aquatic visitor from another world is threatened by a criminal gang. In the second Robby Hoenig adventure, Secret Under Antarctica, a scientific expedition becomes a race to stop a terrorist plot for world-wide disaster, buried beneath the ice of the South Pole. In the third Robby Hoenig adventure, Secret Under the Caribbean, the key to a baffling puzzle - and the truth about a mysterious monster - are locked inside a sunken Spanish ship.