The novel is about a man who works at an agency for people with advanced senses who use them to foil art thieves and bank robberies, and throughout the course of the story the protagonist becomes more and more paranoid as he is continuously foiled by a cat burglar who knows which poisons he is weak against. He believes his girlfriend is cheating on him, and gave away his secret, but it turns out she Is the cat burglar. The infidelity is a lie planted by his best friend, who is secretly a mobster trying to get revenge for a robbery he foiled.
I distinctly remember one specific scene, where he hits a man in the face with a large dildo.
This was actually solved on a different platform! Its Mine All Mine by Adam Davies