Plot summary

The Hardy Boys and Chet Morton fly to Iceland to look for Rex Hallbjornsson, a sailor owed a payout from an insurance company. Before they leave Bayport, someone attempts to kidnap Frank. An American astronaut has disappeared in Iceland while studying the volcanoes. Frank finds a glove which may have been dropped by the astronaut next to a sulfur pit. The Hardys take a flight on a private plane to Akureyri. The pilot is an enemy and forces a landing on a glacier, where the Hardys are fooled by a phony rescue helicopter that picks up the pilot and leaves them behind. They try to use the radio, but the pilot has hidden the frequency crystal. They find it and make contact with the radio tower at Reykjavik. Another helicopter comes to pick up the Hardys. They go to Akureyri and visit a phony Rex Hallbjornsson. Returning to Reykjavik, they see Chet wandering in front of the hotel with a strange expression. They realize he has been drugged. Thinking someone might be in their room examining their belongings, they rush upstairs and find the pilot and his phony rescuer. Joe tries to grab the pilot, whose wig comes off. It is the phony Rex Hallbjornsson, who gets away with his partner. Chet and Biff Hooper, who has joined the others in Iceland, go to investigate a man named Hallbjornsson who might know Rex, while Frank and Joe go with a coast guard officer to look for Hallbjornsson at sea. After a devastating storm Frank sees a small raft, possibly with a motor, and thinks it might be the criminals. Over the course of a day or two, they put on disguises and act as phony crewmen for Rex Mar (the real Hallbjornsson, who has changed his name). Musselman, the fake Rex Hallbjornsson, is fooled by their disguises until Joe slips up by speaking English rather than Icelandic. The boys defeat the criminals in hand-to-hand combat and have them arrested.

• Publication date: 1969
• Ghostwriter: Andrew E. Svenson
• Summary: In Iceland searching for a man who is owed a reward, the boys come across a plot to foil the US moon project.