While everyone in the book is decidedly gay, it is difficult to tell if there is any horror content. The man the boys meet may be a devil (mostly suggested by the title and the back page), but little else suggests it.
At best we can believe that the 'devil' is an incubus-type creature, capable of enslaving men by having sex with them.
The two 'protagonist' boyfriends of the book are fairly despicable creatures. One drugs a straight pilot and has sex with him; which turns the pilot gay. The other then says it is *his* fault because he should have avoided the pilot so that he wouldn't have tempted his boyfriend.