Just back from their worldwide tour exhibiting the treasure they had found after locating the long lost tomb of Alexander the Great, John Peters and his wife Liz along with their friends Harry Roberts and Meg are entangled in another archaeological mystery, this time in the Mayan area of Mexico. Once more they become entangled with eco terrorists while untangling the mystery of the missing Devil's Dagger, a Mayan treasure stolen from the National Museum in Mexico City and which is the key to finding a lost underwater city.