Castle and Beckett awaken to find themselves in a darkened room, lying on a mattress on the floor. What's more is they find that they're handcuffed together, their phones and wallets missing, as well as Detective Beckett's badge and gun. They try to remember how they got there, but everything's a blur and they realize they've been drugged. They try to piece together what happened, but the last thing either of them remembers is meeting at a seedy motel that morning to investigate a dead body in one of the rooms. In a flashback, Beckett escorts Castle to the victim's room, to find Lanie and Esposito already there. They fill them in on what they know so far: the victim has a needle mark on his arm and yet was suffocated. Also, the victim checked into the motel under a fake name, Esposito couldn't find a wallet, and the victim's fingerprints were scorched off, making ID difficult. Back in the darkened room, Castle and Beckett continue trying to recollect the events leading up to their kidnapping. Castle recalls that they eventually ended up in the morgue, talking to Lanie about the dead body. In another flashback, Lanie informs them that the fingerprints are too damaged to get an ID, but offers to try to retrieve prints from under the epidermal layer, warning that it could take a couple of days. In the meantime, she gives Castle and Beckett a piece of an envelope the victim had with him. On the back of it is an address for a café, as well as a time when he was presumably supposed to meet someone there. While Beckett has Ryan and Esposito show the victim's photo around the café, she and Castle puzzle over why someone would go to the trouble of erasing the victim's identity. That's when Castle notices a barcode on the other side of the envelope, and says that the barcode is a machine-readable way of identifying an address. Back in the darkened room, Castle and Beckett recall that they contacted the post office, and that the barcode led them to a house in Queens. In yet another flashback, Beckett and Castle snoop around the house, finding it empty, save for a stack of bills piling up. They hear a woman's voice pleading for help, and find an old woman locked up in a cage in one of the rooms. However, as they try to rescue her, she smiles evilly at them as they're drugged from behind and everything goes dark. Once more in the darkened room, Castle and Beckett say that the old woman is the last thing they remember, and try to figure out what's going on.
Meanwhile, back at the precinct, Ryan informs Esposito that he and Jenny will be spending the upcoming holidays with her grandmother in Florida, and that Jenny thought it'd be a good idea to drive down instead of fly. Esposito remarks that it's a relationship test, and that Jenny just wants to confront Ryan about any doubts he's having while leaving him with nowhere to hide. Just then, Captain Gates asks for an update on the investigation. They tell her a waitress at the café recognized the victim, and that the victim was there with a long-haired man with a goatee. They have the waitress working with a sketch artist, and in the meantime, Gates tells the guys to keep her apprised. Then, with Gates gone, Ryan and Esposito go back to talking about Jenny. Esposito warns Ryan never to go canoeing with Jenny, as it's a test to see if he can compromise in a marriage. Back in the darkened room, meanwhile, Castle and Beckett go around in circles (much like a canoe where two people can't compromise), arguing over their next move. Castle accuses Beckett of always having to lead, and that everything's a competition with her. Eventually, they get to a light switch, finding the walls are made up of cinder blocks and the door is made of steel. They also find a huge freezer in the room with them and a hatch in the ceiling, with Beckett getting the idea to move the freezer so they can reach the hatch. Meanwhile, at the precinct, Esposito gets off the phone with Lanie, informing Ryan that the victim was heavily sedated before being smothered. Then, noticing Beckett and Castle still haven't returned, the guys start to get worried, and ask Dispatch to run a trace on the transponder in Beckett's car. In the meantime, Beckett and Castle try to push the freezer, only to find it won't budge. Realizing something heavy's inside, Castle sets about trying to pick the lock on it so they can see what's in it. Meanwhile, Ryan and Esposito locate Beckett's car, abandoned under a freeway. Esposito notices a camera nearby, and has the footage pulled. On it, a guy drops off Beckett's car, before being picked up by another guy in a pick-up truck. Unfortunately, they're unable to get a license plate off the truck. Back in the not-so-darkened room, Castle has no luck with the lock, but comforts Beckett that at least they've been gone long enough that their colleagues are starting to look for them. This seems to cheer her up, and she encourages Castle to keep trying the lock. In the meantime, Ryan and Esposito are at the morgue, now desperate to ID their victim, but there's little else Lanie can tell them except that he spent a lot of time sitting, possibly driving a forklift. Ryan gently urges Lanie to try recovering the prints sooner than a couple of days, and she agrees, despite the risk of damaging them beyond recognition. Meanwhile, Castle finally gets the lock picked, and they find some bloody knives and a bunch of heavy manacles inside.
Worried what they've stumbled onto, they start emptying the freezer, now even more motivated to get out of there. Meanwhile, Lanie tries to recover the victim's prints, with Ryan and Esposito hovering over her. The print tears, but Ryan gets the idea to use part of the print and combine it with partial prints on the envelope. It works, and they ID the victim as Hank Spooner, a truck driver from San Antonio. As they're filling in Gates, the long-haired man the victim was last seen with walks in, and identifies himself as DEA Agent Chuck Martinez. He explains that several times a year, Spooner would drive his rig from a border town in Texas to New York, and Martinez and his fellow agents assumed he was smuggling drugs from Mexico. He says when they went to set up a sting to use as leverage to get Spooner to talk, Spooner made them and instead wanted to talk to Agent Martinez about getting out of the smuggling business. Spooner was afraid of retribution from his employers, and offered to talk in exchange for protection. Unfortunately, by the time Martinez's bosses approved it, Spooner was already dead. Just then, Gates gets a call that Spooner's rig has been found at a truck stop. They head to the truck stop, finding a crate inside the rig with air holes and bits of someone's (or something's) hair. Behind the crate, they find a pool of blood. Back in the not-so-darkened room, meanwhile, Castle and Beckett climb on top of the freezer, but can't quite reach the hatch. So, Beckett prepares to climb on Castle's shoulders, but first, Castle demands she remove her boots. Afterwards, Beckett manages to reach the hatch from on top of his shoulders, just as one of the kidnappers pulls it open, startling them and causing them to fall back onto the mattress. Meanwhile, back at the precinct, Ryan and Esposito did a little more digging on Spooner, including that he took small jobs to justify his smuggling trips, but they're unfortunately no closer to finding Castle and Beckett. Suddenly, Ryan notices the barcode on the envelope, which leads them to the same house in Queens where their colleagues were abducted. They conduct a raid of the house, finding no signs of either their colleagues or the kidnappers. However, they do find a hatch in the floor that leads into the basement. Unfortunately, it's empty, save for a couple of chairs.
Meanwhile, Castle and Beckett are trying to get the cuffs off, when they overhear one of their captors haggling with another man. They're discussing an apparently beautiful woman kept in the next room, and that's when Castle and Beckett realize they've stumbled upon human trafficking. Back at the house in Queens, meanwhile, Esposito says that the hatch was a recent addition to the house, while Ryan says that the bank foreclosed on the house's owners six months ago but that a pair of brothers had moved in recently. On top of that, one of the neighbors recalled seeing Spooner's rig parked at the house recently. Meanwhile, Beckett finds a weakness in the wall, and she and Castle try to exploit it to rescue the woman in the other room. Back at the precinct, meanwhile, Ryan informs Esposito that the house was foreclosed on by National Bank, and that the smugglers must've been squatters. Remembering something from Martinez's files, Esposito says that the feds had raided another house that had had a hatch installed, and that the house had been foreclosed on by National Bank as well. Realizing the smugglers are using distressed properties with a basement, Esposito asks Ryan to procure a list of National Bank foreclosures. Meanwhile, Castle and Beckett work together to tear through the wall, at first hacking at it with knives from the freezer and then kicking it in tangent. Finally, they create an opening big enough for Castle to stick his head through. However, what he finds on the other side is not a beautiful woman, or even a woman at all. Instead, he finds a tiger, and quickly pulls his head back through the opening.
Beckett realizes they've stumbled upon animal trafficking and not human trafficking, and that the manacles and knives were for the tiger. Castle, however, is a bit more worried about the hungry-looking tiger getting into the room. Meanwhile, back at the precinct, Ryan and Esposito inform Captain Gates that they've been able to narrow it down to 11 properties in the outer boroughs that fit the smugglers' needs. As NYPD searches those houses, the tiger keeps widening the opening with her teeth and claws. Beckett and Castle try to push the freezer to cover the hole, but when that doesn't seem like a viable plan, Castle comes up with another one. He and Beckett turn the freezer on its end, directly underneath the hatch, and climb on top of it. However, Beckett informs him that tigers can actually jump pretty high. As the tiger gets into the room and starts trying to figure out how to get to her prey, Ryan and Esposito start searching an industrial warehouse that's on their list. They're about to give up and leave, when they hear Beckett and Castle yelling for help. They find the hatch and their colleagues, but also find the old woman, who has a shotgun pointed right at them.
They tell her to drop her weapon, but her two sons pop out, guns also trained on them. While Ryan and Esposito get into a stare-down, the tiger circles Castle and Beckett, before finally jumping high enough to knock the freezer over. Ryan and Esposito decide saving their friends is more important, and let the old woman and her sons go. By the time they reach the hatch, Beckett and Castle are nowhere to be seen; instead, Ryan and Esposito find them clinging to a pipe in the ceiling and manage to get them out of there. Meanwhile, the old woman and her sons try to make a getaway, but Captain Gates shows up just then with backup and arrests them. Gates then returns Beckett's badge and gun, informing her and her colleagues, much to their chagrin, that she's now instituting a new policy: no one goes anywhere without calling it in first. At the precinct the next day, Agent Martinez informs Castle, Beckett, and Gates that the old woman is named Ruth Spurloch, and that she and her sons have been selling endangered tigers to wealthy clients all over the world, making millions off their breeding farm in Texas. Martinez also informs them that he'll be turning the case over to Customs and the FBI, and that they can coordinate their murder investigation with them. Then, as Gates walks Martinez out, Ryan and Esposito confirm that the hair in Spooner's rig was from a tiger and that the blood they found was from raw tiger meat. Beckett then gets ready to leave, as she and Castle discuss their crazy brush with death. Castle says there's no one else he'd rather be handcuffed to (only, he accidentally says 'hitched'), and Beckett returns the sentiment, teasing that next time they should do it without the tiger.