We open with Shaw in black lowering himself into a vault with a gold Aztec-looking mask on a pedestal in the center; a bolt falls onto the floor from his descent rig and sets off the alarm. The vault closes and the air is siphoned out of the room. Shaw asks Casey over the com, “Is the Intersect busy?”
Hannah is telling the Intersect she wants him to teach her, but what she had in mind was NOT for Chuck to run off after Sarah. She asks Morgan about him, mystified at what meaning his continuing relationship with Sarah could have. Morgan, however, is just as mystified, especially when Chuck says he has to run off on a Nerd Herd emergency. Morgan is the assistant manager – he should know before Chuck about any repair calls. Hannah runs off after him, ostensibly to shadow the emergency. As he goes to work on the server Hannah walks in. Chuck is shocked but forced to have Hannah help him. The fix works, Shaw is saved. Chuck and Hannah are hired on the spot by the curator to ensure that there are no snags at the unveiling of the mask the next night.
Shaw brings coffee for Sarah the next morning, who appears nervous. Chuck is briefed on the mask and other artifacts, which are being used to smuggle Ring items into the country. Chuck insists he can handle Hannah during the next attempt to swap the mask. Morgan shows up at the Ellie’s apartment and tells her he thinks Chuck is drowning his sorrows in video games.
At the exhibit opening Shaw makes Sarah uncomfortable on the floor while Chuck and Hannah make themselves comfortable in the server room. Hannah tells Chuck that she took the job at Buy More because of him and kisses him, but breaks off when she sees Sarah on the security video. She thinks Sarah’s trying to make him jealous with the “exceptionally good-looking” date. Before Chuck can make up an excuse, he flashes on someone else on the video in the room: the Ring agent who broke in previously to place the contraband inside the exhibit before it traveled to the U.S. He runs off to warn Shaw and Sarah but Hannah sees Chuck appearing to confront Shaw on the video feed. When Shaw leaves (he has a long-standing conflict with Vasillis and his cover would immediately be blown) Hannah becomes even more stressed, sensing conflict in this new triangle.
Chuck and Sarah sneak off to switch the artifact with a reproduction before the vault opens to the crowd. Chuck remotely shuts off the server and when the alarms go off Hannah sets to work trying to fix it, as the museum curator panics in the background. As Chuck and Sarah fight off the Ring agents inside, Hannah succeeds in overriding Chuck’s shutdown and the vault begins to open with Chuck hanging in plain view. Shaw closes it again from the van, and a tug-of-war goes on for several moments; Chuck gets out with the mask just as Hannah shuts Shaw out of the system and the crowd enters the vault to view the mask. Chuck tries to smooth things over with Hannah but she “knows” he left her to fight the battle alone while he carried on with Sarah elsewhere. She tells him things will have to be strictly professional between them from now on and stalks out of the control room.
Ellie enters Chuck and Morgan’s apartment and asks Morgan what he’s found out about Chuck. He proposes an intervention, but Chuck interrupts and the pair leaves for the Buy More. Vasillis, meanwhile, has tied up the curator and reviews the video, spying both Chuck’s moves on Hannah and his switch of the mask with Sarah. Vasillis calls Buy More and pretends to be from the museum, and Morgan sends Hannah back for further work on their alarm server. Shaw brings coffee to Sarah and she verbally unloads on him. When Casey comes by and thanks Shaw for the coffee, however, she is taken aback. Vasillis locks Hannah in the vault. The air begins to run out and Vasillis calls Chuck and tells him he knows who he is – and Hannah has fifty minutes of air left. Back at Castle Shaw and Sarah succeed in opening the artifact and in springing the trap inside: poisonous Cyclosarin gas.
Chuck grabs Casey and they head to the museum to rescue Hannah and get the antidote that Vasillis must have. Chuck and Casey decide to fool Vasillis into thinking he’s been gassed to get the antidote. Shaw and Sarah apologize to each other for the emotional battle, thinking the end is near. Chuck stalks into the museum and threatens to deploy the weapon. Vasillis and his men balk, and Chuck sets off the grenade, resulting in panic – Vasillis doesn’t know which artifact contains the antidote. Chuck flashes on the vase containing the antidote, smashes Vasillis in the head with it to get the antidote, and tells Casey to save Sarah and Shaw while he frees Hannah from the vault. Hannah awakens in Chuck’s arms, sees his fear at the prospect of losing her and is reassured that he cares for her. Shaw carries Sarah into the museum just in time to receive the antidote. Vasillis has recovered consciousness and, from hiding, sees Shaw holding the still-weak Sarah. He realizes he was duped and escapes.
Back at Castle, Chuck is warned that the training wheels, Casey, Sarah and Shaw, are going to be coming off because of his success (implied: and because of his lack of panic this time around!). Chuck and Sarah begin the emotional task of dissolving their relationship. Morgan opens the Buy More to let Ellie in for the intervention after closing, when Chuck has returned. They catch Chuck in the entertainment room, kissing Hannah. They back out unseen, Ellie relieved, Morgan wearing all the conflicted feelings that Chuck, Sarah and Hannah were dragging around until now. Back in Castle Casey shrugs out for the night, leaving Sarah and Shaw alone and Morgan walks out of the Buy More with a melancholy slouch in his step and a sweetly rolling guitar ballad in the background.
The music takes an ominous turn as Vasillis appears in a spotlight in the dark before the Ring leaders to report that Daniel Shaw is alive. A voice silhouetted by the light tells him that Daniel Shaw will meet the same end as he; a gun is placed at his head, the trigger pulled, and Vasillis falls to the floor as the camera fades.
