The Baptiste season finale opens with Stratton, still in his safehouse with his dead ex-wife and her husband. Their assassin, Nicolai, isn't dead yet, but as Edward points out when he wakes up, he will be if an ambulance isn't called. What does Edward want in exchange? Cristina's freedom. He's still trying to be the hero, with a line of dead bodies behind him. But Nicolai knows nothing, pointing him towards those who are already dead: Kim and Constantine. Stratton leaves him to die and heads back to the Netherlands determined to find and rescue Cristina.
Greg: My capacity for believing things I didn't think were possible has recently expanded.
After the realization that Martha is probably the mole in their investigation, Baptiste has gone to her apartment, frantic to get ahold of her. Genevieve thinks this is insanity, but Baptiste says he has to know. Their efforts bring them to Niels, drunk, and combative over the revelation Baptiste is his father. (Genevieve's face y'all. She did not ask for this twist to be thrown at her any more than the rest of us.) But one thing about Baptiste is he's dogged. He spells out the evidence Martha is working for the Brigada Serbilu, much to Niels' shock. The soap opera of his life contains many things, but his mother informing to Romanian gangs is not one he's willing to entertain.
He does tell them where she is: Yoga. When they rush her outside the studio and Baptiste starts telling her about the death of Edward's ex-wife, she seems shocked and says she'll get in touch with Scotland Yard. She doesn't realize they are serious when they say they think she's working with The Brigada, snarking about "her Romanian gang friends" to Genevieve. But the amusement soon falls away, as Genevieve points out that Europol is making headway everywhere but here, and this would explain why. Martha isn't that shocked Genevieve might believe it. But she's genuinely surprised and hurt Baptiste would. He admits he doesn't know what to think.
As they drive away, Baptiste is trying to put together something in his mind. But before he can tell Genevieve, the Brigada Serbilu smash into the car, chasing them through Amsterdam's streets. It's an odd bonding experience, but surviving seems to bring Genevieve and Baptiste to an understanding. Stopping at a gas station, Genevieve notes the Brigada came at them right after they left Martha. But, standing there, Baptiste has a brainwave. Something about Niels and the trip to find Herman. He needs more information -- and he knows who might have recorded it.
Hilariously, Visser has dismantled his setup, just as Baptiste demanded, but all the equipment is blessedly still there in the dumpster, including the hard drives. Digging through the footage from the bathroom pit stop during his trip with Niels, Visser finds the first half of a phone call Baptiste heard that seemed innocent at the time. But it turns out to have been a call to his Brigada superiors, where he says he'll take care of "that b*tch" (meaning Kim), and that no one should worry, they are very close to getting the money. Martha is innocent; her son has been using her all this time.
Baptiste and Genevieve head to Martha's, not to apologize, but to tell her their suspicions. She reacts like a mom and a cop, demanding to see their evidence. Do they have proof? (Obviously not, since they're asking her for a key to his house instead of getting a warrant.) She doesn't want to believe it, but when Baptiste asks if Martha mentioned to Niels about calling Baptiste in the U.K., she becomes uneasy and agrees to go with them to her son's apartment. But when they arrive, she won't go inside. Back at the bar, Niels' Brigada underling (he has underlings?) has to admit Baptiste and Genevieve are still alive.
Stratton apparently missed the plot point where Kim died. Upon learning of her passing, he decides to talk to Greg in hopes of finding a lead. Greg points him towards the box Kim left behind. Stratton points out that she must have left this for Greg for a reason. Considering what she'd done in her former life, to have stayed in Amersterdam must have meant she had an insurance policy. As he digs through the box, he realizes this is all the evidence they need to bring down the organization.
At Niels' house, there's a drawer full of evidence. Looking out the window, Baptiste sees Martha on her mobile and realizes she called Niels to warn him. He races down and pulls the phone from her ear, as she protests: her son is all she has. Niels is unapologetic; sneering Baptiste has to deal with the reality that his own flesh and blood is one of those monsters he's spent his career chasing down. As Baptiste grapples with the horror, Stratton calls, with the evidence he found at Greg's, including coordinates for somewhere on a map.
Baptiste drops off Genevieve at her apartment, where Niel's Brigada henchman was just seen entering. Walking in, she notices one of her figurines is out of place and realizes she's not alone. But her would-be-assailant is already gone. Her phone rings: Niels' operation has been cut off, the Brigada put a price on his head. Genevieve calls Baptiste, and they agree they should try to find Niels since he could give them inside info on the inner workings of the gang. But first, rest.
For the show's final scene, the action jumps ahead two months, to Deal, with Stratton and Baptiste on the beach. The coordinates did lead to the captive girls, but Cristina was not among them. She'd been sold for 750 euros. As for Niels, Martha agreed to meet with him, bringing a forged passport to get him out of the country. But it was a setup, to take him in for Europol. In hysterics, he took his mother hostage, and as she fumbled in her purse for her weapon, he shot her in the head. Frantic, he took aim and shot Baptiste in the shoulder before the Europol team took him down.
It's not a happy ending for anyone, just death, and sadness. But Baptiste is done thinking he's ready to retire...