While getting coffee at the station, Dan and Jack meet Samantha, who's just been hired as a lab assistant in the CSI unit and can't wait to do fieldwork.
That night, Jack returns home, finds something wrong with the lock, and discovers his uncle Nate inside. Jack's not happy - he hasn't seen Nate in 15 years - and Nate asks him if he's still upset about "that thing with the dog." Nate tells Jack that he thinks he witnessed a crime yesterday.
Nate says he saw a house catch fire and a man running away from the blaze. He didn't report this to the police because he "might have an outstanding warrant." Nate explains that he'd been selling insurance, but when a claim arose, he discovered his employers had run off with the money. Jack doesn't buy this and arrests Nate for insurance fraud.
The next day, Jack tells Liz that uncle Nate is a con artist who swindled Jack's parents, which caused them to lose their home and forced them to move into a pet-free apartment, so young Jack had to give up his dog. Liz is sympathetic but says she's less interested in busting Nate for insurance fraud than prosecuting a major arson case.
Jack and Dan interrogate Nate, who claims to have overheard a barroom conversation about arranging a fire on Cedar Hill Lane - and that he's bought Jack a replacement dog, which he warns is an ankle-biter. But if Jack doesn't pick it up, the dog will be put down. When Jack brings the dog home, it bites his ankles.
The partners visit the torched house and find Samantha - she'd checked out the police log - who's already determined that it was an arson job. They notice that the neighborhood is deserted, but Samantha says she saw a pretty blonde woman driving away from a nearby house, carrying a shotgun.
As Jack and Dan check out the house, a car heads straight for them. A busty blonde jumps out, fires a shotgun into the air, and tells them to get off her property. Once Jack and Dan prove that they're police, the woman, Miss Bukowski, explains that people have been trying to run her off ever since she refused to sell her house like everyone else did.
In a flashback to a day earlier, we see the Kettleman Corporation wants to develop the area, but it has to be totally vacant, and a man named Kenny Griffin, who is fond of playing with matches, promises the suits that'll happen. Meanwhile, Jack assures Bukowski that a patrol car will be by, while Dan personally promises to protect her body.
Liz tells Samantha that her findings are inadmissible, but Jack convinces Liz that they constitute probable cause. Then he finds Dan getting intimate with Bukowski. He also finds a man spreading gasoline around the house. When Jack draws a gun, the man throws a flaming torch at him, which Jack catches in midair, as Dan bursts out of the house and subdues the man, who confesses that he got $50 and a bottle to set the fire.
While Jack discovers that all the vacant houses were sold to the Kettleman Corp., Bukowski tells Dan that she saw two guys hanging around - and one of the men matches the description of his uncle. Nate admits knowing Griffin and his arsonist ways but claims he didn't realize what he was getting into. Liz and Dan want to use Nate to set up Griffin for a sting. After an evening doing shots with Liz, Jack reluctantly agrees.
Dan and Nate go to a bar, where Dan's favorite snitch, ex-pawnshop owner Julius Grant, now works. Julius overhears their conversation; he knows Griffin by reputation and is scared to death.
Dan - posing as a developer - and Nate meet Griffin, while Jack watches. Offered $10,000 to torch a property, Griffin refuses the money. He'd rather pay the owner "a persuasive visit" first. Dan, not having an actual property problem, gives him Julian's name and the bar's address.
When Jack, Dan, and Nate ask Julian to play along, he refuses. But when Griffin shows up, Julian tries, but caves. Dan convinces Griffin that Julian's known to say no when he means yes. Griffin gets frustrated, and tells Dan he'll torch the place for $100,000. He's holding a fundraiser at his home tonight, so they can give him the money there.
Dan, Nate, and Jack - working surveillance - go to the party. Dan and Griffin do the deal, while Jack gets this on tape, but Griffin discovers that the money is missing because Nate took off with the cash. When Dan pulls his gun, Griffin disarms him, knocks him down, and runs.
Dan and Jack give chase. Griffin surprises Dan from behind and punches him out. Griffin also overtakes Jack from behind, grabs his gun, and handcuffs him. Dan confronts Griffin, who threatens to kill Jack and take Dan hostage. Dan tells Jack to remember his dog, so Jack bites Griffin's ankle, which enables Dan to disarm and arrest Griffin.
Jack is angry about the missing money, but Dan - knowing that Nate was a con man - switched the cash for paper before they went to the party. Meanwhile, Nate discovers that he's got nothing but a note from Dan to stay away from his partner.
Jack then presents Bukowski with the ankle-biting dog and finds self-proclaimed "guard dog" Dan is already there, keeping watch over the lovely lady.