April and Mark are on a Caribbean island searching for Professor Antrum, a scientist. Antrum has discovered a cavern that goes down to the remains of the lost continent of Atlantis. Thrush (led by Colonel Frank Faber) is interested because the cavern contains crystals that, when exposed to sunlight, generate enormous heat and destructive power. The cavern is on the property of Le Gallows, an eccentric who likes to dress like a 17th Century French nobleman. April suspects Le Gallows may also be aligned with Thrush.
—Bill Koenig