Professor Alfred Bottoms has called the characters to London, regarding some issue in Libya, but when they arrive he asks them to look into an issue for Inspector Reginald Fox, of Scotland Yard.
There have been several reports of pedestrians being attacked while walking through Hyde Park by a strange frog-like creature wielding a trident and net. Tracking down the leads with some Investigation by the Professor of the scene of the crime points to all the victims coming from one of several government buildings in the area.
Some Streetwise contacts from Sir Malcolm and the characters determine they all worked at Kensington Palace. As the rumors of the attacks spread, they seem to get wilder with each retelling. The characters use Persuasion to get a uniform from the Palace, but only manage to get a single one.
Goldie 5000 is chosen as the bait, while the others hide in the bushes. When Goldie is attacked, they surprise the frog creature, but it leaps away and dives into the lake.
Using their contacts in Section X, the characters obtain several experimental diving suits, and follow the creature through a tunnel to the river Thames, where they discover a parked submersible.
Entering (the occupants were not expecting to be followed), they find several frog-like diving suits of foreign origin. Moving further into the sub they encounter the occupants, a small force of Beligian soldiers.
In an epic battle, the heroes defeat the captain, Siaak Theodore, although Goldie is badly damaged (and later will need repair). The Professor uses his device to read the foreigner’s mind and learns the Belgians planned to impersonate some of the Palace staff and steal valuable artworks; in fact two more of the staff have been captured and were being held in another locked room on the vessel.
The heroes hand the infiltrators, and their vehicle, over to the authorities.
For their trouble, they receive a commendation from the Royal Court (3 favors each, for the major prize) and £1,000 as a reward (£333 each). Characters got 1 Experience Point each.