After a sniper's bullet kills a tow truck driver, the truck careens into Karen Stottlemeyer's car as she is making her way to work, sending her to the hospital. As Captain Stottlemeyer grapples with the possibility of losing his wife, Lieutenant Disher speculates that an ongoing local union dispute may be behind the shooting.
Eager to find the person responsible for nearly killing his wife, Stottlemeyer confronts union leader Harry Bolston at a union rally. Bolston denies any wrongdoing, and Monk believes him, suspecting something just isn't right. But Stottlemeyer's clouded judgment has made him obsessed with nailing Bolston and the union.
Meanwhile, Sharona has captured a lost dog at crime scene, which eventually leads Monk and Sharona to the doorstep of Evan Coker, the dog's owner. While Sharona is flirting with Coker, Monk is distracted by a neighbor's miscalibrated sundial.
A few days later, a second shooting of another tow truck driver prompts the Captain and the SFPD to go full-force after Bolston and the union - that is, until Monk calls. He knows the union had nothing to do with Karen's accident.
Monk and Sharona have Stottlemeyer and Disher meet them at the police impound lot where the first shot-out tow truck is being kept. There, Monk explains that the car the truck is towing belongs to Evan Coker, the owner of the lost dog Sharona found. After finding traces of gun oil in the car's glove compartment. Monk suspects that Coker was concealing a weapon there, and Monk and Sharona decide to pay Coker another visit - this time with Stottlemeyer and Disher in tow.
Stottlemeyer is running out of patience and wants answers immediately, so he brings in a task force to search Coker's house. The search turns up nothing. Meanwhile, Monk begins looking around at the neighborhood, and notices a municipal garbage truck. That's when it hits him - it's trash day, and Coker must have thrown the evidence away! Monk races after the garbage truck and starts pulling bags out of the compactor, and when Disher and the task force sift through the bags, they find a handgun.
When Disher IDs the gun as the same weapon used a week earlier in a bank robbery that also resulted in a murder, the case comes together: Coker was the robber/murderer, and had put the murder weapon in his glove compartment. When his car got towed, he was forced to shoot the tow truck driver in order to get the gun back and avoid the possibility of it ending up in the hands of the police. He then shot another tow truck driver to try and keep the cops focused on their union murder suspects - and off of his trail. The evidence is enough to put Coker away for a long time.
When Stottlemeyer brings his wife home from the hospital, he considers would it would have been like to go on without her - and realizes he's just gotten a glimpse of what Monk has to deal with every day. In the end, not only is the Captain brought closer to his wife, he gains an better understanding of Adrian Monk.