Mr. Cromarty was a mercenary that worked as an enforcer for black market dealer Margaret Astor.
Mr. Cromarty was employed by Margaret Astor as an enforcer and mercenary for many years.
After Santino Scarpatti hired Antonio Miele to steal the skull of Saint Peter, Margaret sent Mr. Cromarty to kill Miele and steal the skull for her. Mr. Cromarty managed to track Miele to the Patricia Hotel where he murdered Miele and ransacked his room in search of the skull.
Shortly after his murder of Miele, Sam and Dean Winchester arrived and Mr. Cromarty confronted them at gunpoint with a fake police badge. Mr. Cromarty forced the Winchesters to handcuff themselves to the radiator and resumed his search of the room, ignoring the Winchesters demands to know what department he worked with, where his partner was and their reminder of the dead body in the room. Finding nothing, Mr. Cromarty left the room and ordered the Winchesters to stay where they were while he called it in.
After Mr. Cromarty left, the Winchesters recognized that he was in fact a fake cop, but figured that he probably would call the murder in to try to frame them. However, Sam carried handcuff keys on him and was able to free himself and Dean.
After Father Luca Camilleri ambushed Sam and stole the paper carrying the tracking number for the package containing the skull, Mr. Cromarty ambushed Luca, knocked him unconscious and stole the paper. Mr. Cromarty was able to use the tracking number to locate the package containing the skull at the shipping office. Unknown to Mr. Cromarty, the Winchesters got the tracking number from Luca who had memorized it and followed it to the same location. The Winchesters and Luca then trailed Mr. Cromarty as left the shipping office.
Not realizing that he was being followed, Mr. Cromarty traveled to the warehouse where Margaret intended to auction off the skull to Santino Scarpatii and Santino Scarpatti's Bodyguards demanded to know why Sam was there, causing Sam to explain that he was there to join the auction and revealed Lucca's money. After the various offers are collected, Mr. Cromarty reads them off and is amused by Sam's offer.
After discovering that Greenstreet's offer was zero, Mr. Cromarty drew his gun, only to have Greenstreet offer him a million dollars in cash immediately if he would kill Margaret and hand over the skull. Though Margaret protested that Mr. Cromarty had been working for her for years and wouldn't betray her, Mr. Cromarty shot Margaret in the back, killing her. Mr. Cromarty commented that she should have discussed a raise with him before shooting one of Santino Scarpatti's Bodyguards dead, provoking a firefight between everyone in the room.
During the firefight, Mr. Cromarty primarily exchanged fire with Scarpartti and his surviving bodyguard. Mr. Cromarty managed to hit Scarpatti in the heart with a shot, killing him, but was hit in the right shoulder by a return shot from Scarpatti's surviving bodyguard. Before the bodyguard could fire again, he was shot by Sam, allowing Mr. Cromarty to escape, wounded, to get the drop on Dean who was exchanging fire with Richard Greenstreet's Bodyguard. As Dean killed the bodyguard, Mr. Cromarty tried to shoot him only to be interrupted by Luca. In the struggle that followed, Mr. Cromarty shot Luca before turning his attention back to Dean. Before Mr. Cromarty could kill Dean, he was shot in the abdomen by Sam, killing Mr. Cromarty.
After the firefight, Sam and Dean checked on Luca to find that Mr. Cromarty's bullet had only grazed him. With Mr. Cromarty and most of the others dead, the Winchesters alerted the police who arrested Greenstreet and presumably the sentries Dean had rendered unconscious outside.