After the first party arrives back in their own time (after their abduction by the Great Race of Yith), Jonathan Putnam retires. Now at the brink of insanity, he finances a number of adventurer teams in an effort to regain his own sanity. One of these parties is made up of Joyce Coleman (Archaeologist & specialist in Ancient Greek), Billy Masterson (a farmboy and football star), and Endeavour McQuinn (a detective and putative leader of the expedition). They are tasked with attending an occult auction in Vienna. Putnam purchases first class tickets for all of them on the Mauretania, bound from Boston to Lisbon by way of Bermuda.
As they board, they spot an inept man carrying several books. They later learn his name is Prof. Paterson, and resolve to talk to him later. Perhaps he has experience with the occult.
On board, they encounter a number of odd events. They meet another of Putnam’s adventuring teams, more experienced than themselves, which is headed for Jerusalem after uncovering clues during their investigation of the Cornwallis Mansion on Cape Cod. Prof. Felix Fuda, Hargrove Thorpe, and Richard Bloch have dinner with the party several times on shipboard. Richard is athletic and hits it off with Billy. Fuda chats with Joyce, and Endeavor is unimpressed with Hargrove, who seems an indolent Brahmin.
Endeavour recognizes Count Mikhail Andreevich Kurosov from the newspapers, but the Count’s bodyguard keeps everyone at arm’s length. Billy of course tries to force his way through but fails. Instead Billy amuses himself by following around a scruffy priest who keeps sneaking into the first class decks but who is obviously lower class. He follows the priest down to the 3rd class cabins and is threatened by the priest, who is armed. Billy exits, stage left.
Billy then tracks down Prof. Paterson, who is busy being very seasick in his cabin. Billy breaks down the door, thinking he is saving Paterson, and then apologizes while snooping around the cabin a bit. He is forced out, and later is chagrined to find the door soon repaired by the crew. He had hoped to bother Paterson further.
Joyce, Billy, and Endeavour have dinner with the Captain, who seems eager to escape his guests. Billy again spots the priest lurking, and tells Malcolm Pinkum, the Ship’s Purser, about him. Malcolm promises to look into the affair. The next day, Malcolm assures the party that the priest will not be seen again, ever. The party searches the priest’s former quarters and finds nothing. Endeavour steals a uniform from the ship’s laundry and searches the third class deck for clues, explaining that he is checking for gas leaks. His efforts are largely thwarted by Billy’s insistence of following him around. Since Billy is not in uniform, this raises questions, although Endeavour does enjoy the intimate hospitality of a well-padded female passenger. After that, he soon gives up the chase.
Later, the Count plays shuffleboard. Hargrove is watching from a deck chair, sipping a highball. Endeavour attempts to approach the Count, but just at that moment, two assassins hurl a grenade and open fire on the Count. Hargrove neatly hits the grenade over the side of the ship with a cricket bat, and Endeavour hits the floor, leaving the Count to fend for himself. The assassins soon leap over the side of the boat and flee in a waiting speedboat. The Count takes Hargrove into his confidences, and Endeavour is left checking for wounds on himself (there are none).
Meanwhile, Paterson has recovered and invites the party to observe his crystal ball (a Glass of Mortlan) using an incantation from the Zanthu Tablets. The spell goes awry and a titanic octopoid seems to spot the watchers and move towards them. Paterson hastily ends the spell and ushers the party out, very nervous.
The party spends a lovely day at Bermuda, but after returning they seek Paterson again. He is not seen for two days, and eventually Billy bursts down the door again, only to find Paterson hanged, and a suicide note about elder horrors nearby. The party grabs Paterson’s gear (crystal ball and brass brazier) and books (a modern edition of Nameless Cults, an English translation of the Zanthu Tablets, and Cthulhu in the Necronomicon) and then reports the suicide to the Purser.
The party hears someone outside their room that evening, and Endeavour chases after an ugly sailor who leads him into the bowels of the ship, where five knife-wielding men attack him. Joyce and Billy are still some distance away.