Bailey presents Stark with case #4399: the Vending Machine Vandal. After looking at the file, Stark gives Bailey his take on the broken window theory of crime prevention, which he heard about on a cop show and calls the "broken door theory" because small crimes are the "doorway" to bigger ones. Stark goes on to say that there's always a victim when investigating a crime.
That brings us to an escort named Holly, who's trying to leave town. Unfortunately for Holly, her pimp, Gemini, has shown up. Holly wants out of the business, but in these tough economic times, Gemini won't let his best earner leave.
Meanwhile, Stark and Bailey's investigation into vending machine vandalism leads them to the Ligato Hotel, where Monroe, the manager, has been waiting for them. In hopes of possibly saving a "hot woman," Dan sees some blood, or as he calls it, some of "that DNA stuff" on the broken glass of the vending machine. After talking with Monroe, Jack and Dan get the hotel guest list and begin interviewing potential suspects.
Dan's detective nose starts sniffing as he sees the name of a local who was a guest at the Ligato Hotel. After questioning Paul McIntyre, the detectives learn that McIntyre was at his house all night, but his stolen credit card stayed at the hotel. The detectives agree that he's lying about something, but with no evidence, they head back to the hotel.
They arrive back at the Ligato just as Gemini heaves Monroe off the roof. After successfully getting away, Gemini calls Paul McIntyre and apologizes for the leak in his operation and seeks to make amends by setting him up with an escort, free of charge. Homicide arrives and starts investigating Monroe's murder, and Bailey heads back to the precinct. Meanwhile, Gemini, apparently having caught the flu bug that Stark first gave to Monroe, notices that his watch missing.
Stark arrives at the precinct with the very same gold watch on his wrist, but says, "Let Homicide get their own evidence." After researching McIntyre's credit card purchases, Bailey and Stark know that Paul lied, seeing as how he bought golf clubs hours before his card was "stolen."
The detectives get to McIntyre's house in time for Stark to use his charm in order to prevent McIntyre's wife, Pam, from killing her cheating husband. He urges Pam to divorce him and take all his money instead. While questioning McIntyre, the guys are told about Gemini, and the detectives hatch a sting operation. McIntyre calls Gemini to set up a date, instructing him to send the escort to the Caravan Motel.
Unfortunately, Gemini suspects that McIntyre is talking to the police, since he's moving the meeting place from an upscale hotel to a rundown motel, but he decides to set the date up anyway. At the Caravan Motel, Stark and Bailey stage their stakeout. Holly arrives at Bailey's motel room. Instead of getting Holly to make a move, a nervous Bailey pours his heart out to her about his ex-girlfriend. Growing impatient, Stark moves in.
Unbeknownst to them, Gemini has also been staking out the Caravan. While Gemini and Landry head to the room, Holly explains to the detectives that she hates Gemini and wants to leave him. Gemini and Landry open fire outside the motel room. The guys and Holly head for cover in the bathtub. Homicide and Lieutenant Ana Ruiz arrive on the scene, and she's fuming at the unauthorized call girl sting operation. Ruiz orders the boys to tell everything they know about Gemini to Homicide. Holly overhears the conversation and tells the detectives that Gemini owns a vending machine company that he inherited from his dad. Stark and Bailey ask ADA Traynor to get the financial records for Level One Vending. She eventually agrees, and the records show that the company is owned by Eugene Spellman, Jr. (aka Gemini). Bailey thinks Gemini is using the business to hide income from the escort service. Ruiz informs Stark and Bailey that Hodges and Lang will bring Gemini in for questioning.
Despite Ruiz ordering Bailey and Stark off the case, the guys again disobey her order and wait at nearby Watsun's Pharmacy while Hodges and Lang move in on Gemini. While waiting, the boys go into the pharmacy to get Dan some "medicine," where they just happen to see Gemini picking up his own medication. Five minutes earlier, the pimp had burned down his house in order to keep Hodges and Lang busy so that he could get to a plane.
Despite leaving their guns in the car, Stark and Bailey move in to apprehend Gemini, who escapes the pharmacy - but the chase is on through the streets. While getting choked out by the pimp, Stark handcuffs himself to Gemini.
Afterward, Bailey tells Holly that she can pawn Gemini's gold watch at Julius' pawn shop. At the precinct, Liz informs Bailey that the dirty handkerchief Stark left on her desk turned up a suspect that leads the boys to finally apprehending their vending machine vandal.
The suspect, Ryan Winkler, tells the detectives to send the bill for the vending machine to his uncle, since he owns the Ligato. Stark wants to punch Winkler in the face for being so smug, but Bailey has a better idea: Stark, still flu-addled, gives Winkler a big kiss, compliments of the Dallas P.D.