Daemon Summoner is set in Victorian London, and follows the vampire hunter James Farrington as he attempts to hunt down and kill his wife, Emily, who is a vampire.
The game begins with Farrington chasing Emily through the streets of London and the London Sewers. Farrington nearly manages to defeat her, however while wounded she manages to escape to a nearby forced stealth section in the docks and attempts to board a boat.
Farrington stashes himself aboard the self-same boat and trails Emily to a monastery, where he faces off against the vampire-lord Kinus and his legions of vampires, and witnesses the ongoing war between the vampires and the zombies. Farrington almost defeats Kinus, however victory is snatched from his grasp by the revelation that Kinus had a twin brother. Furthermore, the pair are using a portal in the basement of the monastery to summon Satan.
Knocked out by Kinus' brother, Farrington is transported to an asylum where he is held. In an attempt to escape Farrington discovers that this asylum is also being used to house werewolves, because werewolves are crazy.
A voice in Farrington's head tells him he needs silver to defeat the werewolves. Luckily, someone just happened to leave a revolver and a batch of deadly silver bullets not far from his cell. Much to the NRA's dismay, the box containing the gun is locked, however after aiding a friendly ghost the key is procured and Farrington is once again armed.
Suddenly, Emily bursts out and attacks Farrington, however he defends himself and defeats Emily once and for all. With one mission over, Farrington sets about finishing another: stopping the Kinus brothers from summoning Satan. Unfortunately, Farrington has forgotten the location of the monastery. Fighting his way through a nearby vampire office block, he is fortunate to discover a map detailing its position on lid of a crate on the top floor.
He returns to the monastery and once again fights his way through a horde of zombies, vampires and werewolves who are now there also, apparently. He finds the vampire brothers in the basement, but fails to defeat them in time, and Satan emerges from the demonic portal.
By a stroke of luck, it turns out that Satan is weak to the very bullets that guns use, and Farrington manages to unsummon him using his pistol and save the world.
Daemon Summoner is a by-the-numbers first person shooter that features no daemon summoning mechanic. The game's distinguishing feature is that in order to cause damage to enemies they must be shot accurately in a specific weak spot, such as a vampire's heart or a zombie's legs.
Environments are linear, and filled with the game's four enemy types (vampires, zombies, werewolves and imps) which can be defeated through the games various weapons, such as a dart gun, a knife, a six-shooter and molotov cocktails.
The game is narrated by the protagonist, James Farrington, is written in an extremely serious tone, and is less than an hour long.