Bob Howard works for a secret government agency called the Laundry. The Laundry is an agency located in England, and its purpose is to control and prevent citizens from knowing that mythical creatures and the supernatural exists. The agency tasks Bob Howard to help another Laundry worker, Greg, investigate a farmhouse as they believe there is a unicorn infestation. Unicorn infestations are extremely dangerous as unicorns eat humans and have magical powers. The magical powers vary depending on the unicorn. However, the most dangerous part is that unicorns have a reproduction system similar to mushrooms as they release spores, which allow them to reproduce quickly and in large amounts. The Laundry believes the stable is holding unicorns as the owners have been ordering hefty pounds of meat that are not edible for human consumption. The two men visit the stable, and one of the stable owners, Georgina, reveals that the police want to use these superhuman horses (Georgina does not know that the superhuman horses are unicorns) in the police force. This news shocks Howard as the police made no mention of this initiative. Additionally, the police always work with the Laundry and are in agreement that citizens should not know about the occult. Georgina reveals that police officer John Dudley was the one that signed off on this initiative, and the two visit him. However, they soon realize that John Dudley has been mind-controlled by a unicorn when they arrive. This revelation causes them to realize how serious the situation is as only a mighty unicorn, known as the brood-queen, can glamor people. Howard immediately calls for Laundry workers to exterminate the unicorns and tries to find the brood-queen. The two eventually manage to find the brood-queen in the woodshed. With reports that Ada, one of the stable owner's daughters in missing, Howard believe that the brood-queen is holding Ada hostage, and Howard risks his life to save the girl. Sadly, he discovers that the unicorn has already eaten the girl, and the brood-queen is exterminated. In the end, the Laundry workers successfully puts down the unicorn infestation and Howard returns home.