A woman has a twin brother, Robbie, who owns a cat named Touie. Robbie is about to move to London, and asks his sister to fly Touie from his New York apartment to London and help him move in, and she does. After she runs some errands on her second day in London, she finds both Robbie and Touie gone, and, in their place, a French bulldog who wears Touie's tag. She takes the dog, which she decides to call Gladstone, on a walk, and he leads her to the gate of a psychic shop belonging to a man named Mirko. A stately man opens the gate, and the dog seems to know him. The woman follows him inside, where he sits her behind a screen and tells her to be silent if she values Robbie's life. She eavesdrops as Mirko talks to someone else in Russian in hushed tones, though she can't make out much. Once the Russian man leaves, the psychic returns to her and changes out of a suit into a geeky outfit. He reveals that he is not Mirko, but someone named Kingsley. He presses a button, and the bookshelf opens to reveal a secret door to an underground cellar. Kingsley descends and she follows, and they head through a dark tunnel lined with rows of black market goods — where she grabs an unloaded gun for safekeeping — up a staircase through a food mart, through the streets of London, and finally onto a subway car, where they chat. Kingsley works for an agency in the British government, and is trying to investigate where Mirko and Robbie have gone. He impresses the woman with his keen observation powers, and is able to tell much about her background from her appearance. She, in turn, impresses him with her quick mental math and deductive reasoning skills. Kingsley explains what he knows so far. He had been hired to investigate the psychic Mirko's clandestine dealings, and eavesdropped outside the shop one day, where he heard Mirko talk to a woman in the Surzhyk dialect. Not able to understand, Kingsley called up Robbie, an expert in Eastern European dialects, to help decipher. The two overheard Mirko and the woman, Sarah Byrne, discussing a deal on a red diamond, when suddenly, the two sat up, rustled around, and then went silent. Kingsley left Robbie to keep watch in the shop, and pursued the two through the tunnel. As he caught up to them on the street, he saw both of them were quite unwell, unwell enough not to be suspicious when he offered them a ride to the hospital. Both had been poisoned. The woman, as she took off her wig, was revealed to be a famous opera singer. Then, Kingsley returned to the shop, where he found Robbie gone. Kingsley impersonated the psychic and pretended to be Mirko when a Russian man, Igor, came around to collect the diamond. Kingsley accepted the suitcase of cash but gave Igor a fake crystal off the bulldog's collar. It is Igor that Kingsley and the woman now pursue via the subway. The woman and Kingsley follow Igor through the streets of London, and finally catch up to him in a park. He has realized his diamond is fake, and wants to repent. Igor confesses everything. He was hired by a prominent Russian emigre to assassinate Sarah Byrne. Knowing her affinity for British pastries and himself an avid baker, Igor baked poison into his cakes and set up a food cart outside Mirko's. As planned, Sarah bought two of everything and went in to see Mirko, where both of them partook. But Igor's boss was angry when he found out Mirko was poisoned, too, as only Sarah was to be killed. Igor then realizes he has not only killed Mirko but also a famous opera singer, one of his personal idols, and all for a fake diamond. Distraught, Igor takes a cyanide pill and dies. Kingsley and the woman leave the scene, as they have solved nearly everything. Kingsley explains he had visited Robbie's apartment and found the cat, Touie, dead, after it had an allergic reaction to the chemicals in Robbie's brand-new mattress. He had taken the dead cat and left the bulldog in its place. There is only one thing left to figure out: where is Robbie? The woman is worried, as she knows that Igor's poisoned bakery cart had been in front of Mirko's, and she knows her twin brother's love for sweets. But Kingsley's powers of observation come in handy once more: he notices the woman pick the sultanas out of her trail mix, and remembers Igor saying he had baked sultanas into all his pastries. Robbie also hates sultanas, so he must have passed on the baked goods. Indeed, at that moment, the woman gets a text from Robbie which says that he had had an allergic reaction to his mattress and had gone to the hospital briefly, but is on his way back to the apartment. The woman is relieved, and kisses Kingsley.