The book is set as a series of journal entries, where the unnamed narrator goes back and forth between his life with the rats and his work, in a low-level job at a company that his father used to own.

In these entries, the young man dwells on the hatred he feels for his boss, the stresses of caring for his aging mother, a nameless girl he becomes fond of and above all the families of rats which he has befriended and which he uses for company and companionship.

His "ratman" robberies become a newspaper sensation in the area and the man makes quite a stash of money for himself and for the girl he is courting at work.

The book ends with the young man madly scribbling in his journal about the rats gnawing away at the attic door.

In 2013, Valancourt Books reprinted Ratman's Notebooks in paperback with an introduction by horror author Kim Newman.