It is first seen when David Ruskin steals it from Monk, after figuring out the combination lock. Believing that he himself is Monk, Ruskin sets out in vigilante fashion, eventually holding a man he (mistakenly) believed was Trudy Monk's killer at gunpoint with Adrian's gun.
Later, when John Rollins broke into Monk's apartment, he switched the barrel on Monk's gun, so that Monk had a replacement and John had the real one. Later when Monk took it with him to a warehouse (unaware of the switch) and found Trudy's killer, he aimed his gun at him. After some hesitation, Monk lowers the gun, only to raise it again. A shot is fired, and the man falls to the floor, dead.
Actually, Rollins had stood behind Monk and a shelf and shot him, but had made it appear as Monk did. He then came out and arrested Monk, switching the barrels back while telling him about his rights, making Monk have the handle with his fingerprints on it and the barrel that shot the killer.
When Monk's half brother Jack broke into his apartment, Monk hit him on the head with the box. Later during that episode, Jack takes it without Monk's knowing. When they are being shot at by Daniel Reese, Jack uses it to return fire. 
- The appearance of the gun takes a change from "Mr. Monk and the Actor" to "Mr. Monk Is on the Run, Part 1". In "Mr. Monk's Other Brother", it remains closer to the one from "Mr. Monk Is on the Run, Part 1".
- In "Mr. Monk and the Actor", the combination is revealed to be Trudy Monk's birthday.
- In "Mr. Monk Is on the Run, Part 1", the box does not have combination numbers on the top of it, and it appears the box just pops open (as seen in Monk's theory about how John Rollins framed him). However, in "Mr. Monk's Other Brother", the box has combination numbers on top. The box also looks different overall between these two episodes. Since "Mr. Monk Is on the Run" took place prior to "Mr. Monk's Other Brother," its likely Monk got a new box to ensure someone doesn't try to steal his gun and frame him again.
- Monk's revolver seen in "Mr. Monk and the Actor" is a Smith & Wesson Model 19. The semi-automatic seen in later episodes is a Beretta 92. Both firearms have been common police sidearms.
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