An elderly woman is strapped to her chair and kidnapped from her home by two masked intruders who leave a spray-painted lightning bolt on her wall. Captain Stottlemeyer and Lieutenant Disher immediately suspect a 1970's radical group, the Lightning Brigade.
Dissatisfied with the police investigation, the victim's granddaughter, Julie Parlo, asks for Monk's help. In exchange, Julie, a law student, promises to get Monk reinstated to the police force with a clever legal strategy. Eager to get back on the force, Monk agrees to help.
When Julie's grandmother is returned unharmed, the case is put on the backburner by Stottlemeyer and the police, but Monk persists with his investigation and proceeds to rule out the Lightning Brigade. Monk is certain someone else is behind all the mayhem - but whom?
Monk and Sharona go to see Julie's grandmother to get more details about her kidnapping, and she offers them some new clues that lead them to the home of Harold and Carol Maloney, a snooty suburban couple. Grandma Parlo recognizes a photo of the couple: two weeks ago, the Parlos posted a flier looking for the owner of a stray cat, and the Maloneys responded, claiming that the cat held by the Parlos was theirs.
Monk is ready to close in on the Maloneys, but first, he has to take a police reinstatement test. Julie's legal strategy worked, and now Monk is just one 30-minute test away from rejoining the San Francisco P.D. He knows the material cold, but in a hilarious and heartbreaking turn, Monk's obsessions prevent him from answering a single question.
Despite this setback, Monk continues on the Maloney's trail. He figures out that the couple wasn't interested in Grandma Parlo - they were interested in her chair. Sure enough, when Monk and the crew investigate the Maloney's house, they find the chair, which the Maloneys reveal to be an antique worth millions of dollars. However, when the Maloneys proceed to produce paperwork documenting the origins of the chair, with no counterproof, the Parlos appear to be out of luck... until Monk saves the day. He notices that Lieutenant Disher hasn't been sneezing while inside the Maloney's house despite a severe allergy to cats. Monk deduces that the Maloneys never had a cat, and that it was the Parlo's lost cat flier that must have originally drawn them to the Parlo's house. Fortunately, Julie still has a copy of the flier, which clearly pictures the cat sitting in the stolen antique chair, thus simultaneously establishing the Maloneys as liars and the Parlos as owners of the chair. Another case cracked by the amazing Adrian Monk!