Carrie and Al investigate the death of John Patton, an urban explorer who was found dead and staring at the ceiling of a New York public library. Webster determines that he was poisoned by overexposure to large amounts of C-4, indicating that he may have built a large bomb. With the help of transit authority worker Marty Auerbach, Carrie and Al locate Alex Daniels, another urban explorer and friend of John. Alex reveals that John had begun treasure hunting in the bowels of New York, and that he was particularly interested in the legendary treasure of a painter from the 1920s named Alfred Goodrose. Jay uses GPS data to track John's most frequent destinations before his death, and Carrie, Al, and Alex go exploring. They find a hidden room full of C-4 that is rigged to blow, and they narrowly avoid getting blown to bits. Alex is injured in the process, so Carrie uses her memory to navigate the dark tunnels to an exit and gets help. When she emerges, Webster informs her that she located the remains of another missing urban explorer, Harold Estes, who was previously presumed to be a suspect. With no suspects left, Carrie realizes Marty the transit worker lied to her, and that he is the one making the bomb. Marty finds Al and Alex and leads them into a trap, but they escape and find Carrie. Carrie pieces together all the clues from her memories, figures out the target that Marty plans to bomb, and captures him before he can blow anything up. Throughout the case, Alex flirts quite a bit with Carrie, which makes Al quietly jealous. However, when Alex realizes the connection between Al and Carrie, he backs off.