A jeweler named Vijay Banerjee has been hit and badly injured by a car. In his bag are valuable black diamonds. Lisa and Dan try to bring the gems to his house to put in the safekeeping of his family, but no one answers the door. They visit his store, where a clerk calls Banerjee’s house—again, no answer. They convince the clerk to let them look in the safe; she is shocked when she sees what is missing. Banerjee would never take out the diamonds without security—they’re worth around a million pounds.
So Lisa and Dan go to the hospital to try to learn what Banerjee was doing on the street with such valuable jewels. He is sedated, but mutters something about his family being in danger. Lisa and Dan rush off. It seems that they have a ransom hostage situation.
Also in the hospital is Professor T. His mother has decided to reoccupy her studio at their old home, where he is now living—against her wishes. He has a panic attack as he imagines her forthcoming distractions and annoyances, and falls down the stairs. He calls an ambulance—no sirens, please, he requests.
He gets a leg brace and crutches, and calls his assistant Mrs. Snares to pick him up. His mother has no idea where he is, but calls Snares to set up a lunch. He takes Snares’ advice and escapes while he has the chance.
He holes up at the police station, where Rabbit tries to send him away—they’re in the middle of a hostage situation. But Professor T camps out—he just needs to rest his foot.
The police believe Banerjee’s wife and daughter Priyanka are both being held hostage at their home—both are registered at the house, and their cars are there. A negotiation specialist named Ben Sparrow has been brought in, and recommends that the police wait for the hostage-takers to call—Dan and Lisa have brought Banerjee’s phone from the hospital. Better that the thugs remain unaware the police know about the situation. When they force Priyanka to call her father, Sparrow lets the message go to voicemail, then texts, asking for more time.
Unsurprisingly, Professor T has advice to offer. In fact, he has three golden rules of hostage negotiation. First: give the criminals what they want. These situations seldom turn out well. Sparrow dismisses him.
But Professor T happens to be in the room while Sparrow is not when Banerjee’s phone rings again. He picks up and explains that Banerjee has been hit by a car and the police are involved. That’s the second rule: always tell the truth. Sparrow walks in at the end of the conversation and is furious, threatening to arrest Professor T. Christina removes Professor T and makes him stay in her office, with the door closed.
Now that the hostage-takers know the police are involved, Sparrow sends in helicopters, snipers, people on the ground, and thermal imaging. That last item reveals that there are two additional hostages: Banerjee’s other daughter and her own daughter.
Banerjee’s phone rings again. The hostage-takers will only talk to Professor T. When Sparrow reluctantly allows him to speak with them, he tells them he doesn’t negotiate with anyone holding a child hostage, and hangs up.
Now Christina is angry, too. She begins calling a taxi to send Professor T home—until the young girl and her mother are released. Now only Priyanka and Banerjee’s wife remain in danger. They have been placed in another room, while the hostage-takers become increasingly scared and desperate. Banerjee’s wife tells Priyanka to cut her zip-tied hands free with scissors from a nearby desk.
The hostage-takers call the police again. They demand a million pounds, a car, and free passage—or they’ll start shooting. Professor T tells them he thinks they’re bluffing. Their situation is only getting worse. Plus, Banerjee has died, he says. The third rule of hostage negotiation? Convince the criminals their situation is hopeless.
One thug goes to grab Priyanka, but her mother fights and pulls his balaclava off before being pushed away. Priyanka sees her assailant’s face, and then he pulls her out of the room. A gunshot goes off.
The police rush into the house, and find Priyanka and her mother both safe. There’s no sign of the gunmen. They must know about a service tunnel or something that the police are unaware of—and that knowledge suggests an inside job. Professor T guessed that Banerjee was in on the plan, trying to collect insurance money for the black diamonds, which are easy to sell on the black market. Hence his lie that Banerjee was dead: it convinced the hostage-takers their situation was hopeless.
The situation defused, Christina tells Professor T he must go home sometime. Pointing to a suitcase in her office, he says the same to her. She admits that she and her husband have agreed to spend some time apart. He explodes and tells her that he knew they would never be happy; she responds that there are golden rules to relationships as well, and Professor T never gave her what she wanted or told her the truth, but he did convince her the situation was hopeless.
Except: the whole encounter, or at least the end of it, is an imagined one in Professor T’s head.
Lisa and Dan have caught the hostage-takers by scanning all the vehicles in the vicinity of Banerjee’s house and finding that one is stolen. The gunmen eventually emerged from a hiding place in the cellar to find the police waiting for them by the car.
But Priyanka claims not to recognize either of them as her assailant—even though their fingerprints are everywhere in the house. Turns out Priyanka was the one committing fraud, not her father, who is still in the hospital.
Lisa’s father has his own problems—possible dementia. She takes care of him as well as she can, ignoring Dan’s calls and requests to get a drink.
And Professor T? He tells his mother that she can’t stay at the house—she has him all discombobulated, so much that he guessed the wrong culprit in the fraud case. She dismisses him.