The story follows Moist von Lipwig, who after years of undertaking confidence tricks on others finds himself caught by the guards and is sentenced to death under the alias of Arthur Spangler. After a brief spell in prison he is hung by the neck, but not killed. He is brought before Patrician Havelock Vetinari who insists that he either becomes the new Postmaster or be executed.
Moist attempts to escape but is caught by his parole officer Mr. Pump, a golem and brought to the rundown post office where he meets his two staff; Junior Postman Tolliver Groat and his assistant, the pin-obsessed Stanley Howler. Moist learns that the post office has been superseded by telegraph towers known as "Clacks" which are run by the unscrupulous Reacher Gilt.
Initially Moist attempts to escape his duty, but realises that he cannot get away without overcoming Mr. Pump, so he goes to the Golem Trust to help understand how golems are created and controlled. there he meets Adora Belle Dearheart who he begins to have feelings for. He invents the postage stamp in an attempt to raise money and this proves to be highly successful. He also start a pony express service to neighbouring cities.
While staying in the post office Moist begins to experience visions which show him that some of his confidence tricks led to tragedies for those he conned, which result in him starting to have feelings of remorse for the first time, these feelings are heightened when he discovers that Adora Belle's father, Richard Dearheart was indirectly a victim of one of his cons, and as a result lost ownership of his invention, the Clacks. Moist confesses his past misdeeds to Adora Belle just as the post office is set alight, so Moist sets his own safety aside and runs into the burning building to rescue Stanley Howler. He cannot find Stanley, but does encounter Mr. Gryle, a banshee assassin, who confesses that he killed the previous four Postmasters, and as Mr. Gryle swoops down to attack Moist...