Juliet and Lassiter meet Gus at a vehicle storage yard in the middle of the night. Gus received a message from Shawn telling him that he'd solved the case and to meet him there but Shawn has not shown up and Gus is worried. He should be. Shawn is currently bound and stuffed into the trunk of a moving car. Shawn remembers a lesson Henry taught him as a child, and kicks out the rear light of the vehicle. Through the hole in the trunk, he's able to spot some landmark, and manages to text Gus cryptic descriptions of what he sees. Back at the storage yard, Gus is puzzled by the message. Lassiter finds blood on the ground and they realize Shawn's been shot and kidnapped. Gus calls Henry, who arrives at the scene and insists on helping find his son. So Lassiter and Henry team up to decipher Shawn's text and track him down, while Gus and Juliet retrace the steps of Shawn's latest investigation.
Gus tells Juliet they were working on an ice cream truck accident. Shawn noticed a hole in the gas tank and fresh welding marks on the undercarriage of the overturned truck. He believed the truck was crashed on purpose and wanted to discover why. They found out who serviced the ice cream truck and spoke to a mechanic at the garage, who told them welding is usually used to repair a crack or to reinforce steel, but without looking at the truck in question, he can't say for sure why the bottom had fresh welding. Juliet tells Gus she wants to interview the mechanic herself.
Meanwhile, Shawn manages to pop open the trunk and makes a break for it through the woods, being chased by the driver who happens to be the mechanic. Shawn remembers another one of Henry's lessons about evading a pursuer and successfully loses the mechanic in the woods. He spots a gas station, and runs to the attendant for help but before he can fully explain what's happening, the attendant smashes him over the head, knocking him unconscious.
Luckily, Lassiter and Henry have made progress figuring out the clues in Shawn's text message. Henry notices the kicked out taillight and remembers the same childhood lesson. He knows Shawn got himself out and ran into the woods. Lassiter gets a call from Juliet. She and Gus went back to the garage and were told that the mechanic quit, and stole a welding gun from the garage. Unfortunately, he was using a fake name, so they are unable to track him, but he does drive a distinctive vintage Plymouth Roadrunner. Lassiter says they'll keep an eye out for the car, then he and Henry continue the pursuit on foot through the woods.
Shawn, tied to a chair, regains consciousness as the attendant, Rollins, and the mechanic, MacQuarrie, are in the middle of an argument. Rollins is berating MacQuarrie on his incompetence at handling Shawn. He confirms with MacQuarrie that the truck is ready. The money is almost theirs. He then orders MacQuarrie to kill Shawn, but then changes his mind, deciding he might need a hostage instead. Shawn takes a look around and sees a metal plate with the same weld mark he saw under the ice cream truck. He also sees pictures of MacQuarrie in a special ops uniform and realizes that MacQuarrie is a crack shot. If he had wanted to kill Shawn, he would have. He has a soft side, something Shawn can exploit later.
Back at Shawn's apartment, Gus and Juliet find a pamphlet from the garage. It must have been what Shawn was looking at when he broke the case. The pamphlet says that the garage not only services ice cream trucks, it also services armored transport vehicles. The ice cream truck crash was just a rehearsal for an armored car robbery. Juliet tracks down the schedule and route of a large money transfer, knowing that is where Shawn's captors will be.
At the service station, Shawn is confronting MacQuarrie on the robbery. He tells him he knows he welded the bottom of an armored car to create a soft spot, one that is normally not visible but will provide access to the cash once the truck is crashed and flipped. Meanwhile, Henry and Lassiter have tracked Shawn through the woods to the gas station, but Rollins is able to turn them away by claiming he saw the Roadrunner in question but it drove off down the road. Shawn, seeing them go, convinces MacQuarrie to let him call his girlfriend one last time, since this is the end for him. Shawn calls Juliet instead and words his message in such a way that, once repeated to Lassiter, lets the detective know Shawn was back at the gas station all along. Lassiter and Henry turn back to the station only to discover Shawn gone and MacQuarrie dead on the floor. Along with Gus and Juliet, they race to catch up with Rollins and Shawn en route to the armored truck. Shawn is able to break free and jump onto the hood of Lassiter's car, where he grabs a shotgun from Henry and shoots out the radiator of Rollins' pick up, stopping his abductor cold.