Bad Sam, the former head Dog, is two steps away from visiting the great safe house in the sky. If Lamb doesn't rescue him for a second time, it's curtains for Chapman. In the past, Cartwright turned a Volvo Estate into a crime piñata by stuffing it with cash, guns, explosives, and MI5-issued fake IDs. Cartwright had Sam hand it over to Frank Harkness in Les Arbres to buy a girl, who slapped him. Harkness traded her, a member of his harem, like chattel, in exchange for all those illicit goodies. The smart money says she was David Cartwright's daughter and River's mother. River had fixated on a nursery mural at Les Arbres because he recognized the handiwork of the artist, the same one whose hand-painted birthday cards he'd received as a child. It looks like River's daddy is an abusive, murderous, conscienceless mercenary who tortures his injured sons for cash, as provided by any questionable regime paying. The 23 deaths caused by the Westacres bomb are an unfortunate hiccup caused by "a weak link in his organization,". Meaning one of the sons he bred like puppies and brainwashed. Episode four introduces Harkness, who is shaping up to be Slow Horses' most cartoonish antagonist yet. Hugo Weaving is just a fluffy white cat short of being a Bond villain. Harkness aimed for charm but it's clear that he's a spherical Bad man, as observed from any angle. David Cartwright is now in the custody of Slough House, thanks to Sam and Standish's entertaining double-act. He is on Harkness'. Kill by Midnight Or Else' list, but the éminence grise of the service is also in the back of Jackson Lamb's cab. Last season, Lamb took out two trained killers using a tube of Pringles, so if anybody can protect Cartwright, it's him. Unless Lamb decides to ruin the whole thing off, delivers Cartwright to Taverner, and goes for a curry, which would be equally likely from our hard-to-pin-down lead. Standish wouldn't stand for that, but Lamb got his own way with Catherine, allowing her to get her protest out of her system. She's back in the fold, sitting in on debriefings and rolling her eyes whenever Lamb cruelly pours her a drink. The question is, will Whelan last beyond the season finale, or is Taverner stuck with him? The open-hostilities double-act is always a highlight, and season four could do with much more of it. It feels almost criminal that there are only two episodes to go and we haven't seen nearly enough of Lamb. Oldman's character is a rare commodity and rightly used sparingly, but it's hard not to wish for eight episodes instead of six per season. We are seeing much more of Jack Lowden's River, to whom this season really belongs. His chase through St Pancras revisited this show's very first scene, in which River ran hell-for-leather through Stansted Airport on his failed training mission. This time though, he made it out, only to fall at Emma Flyte's last hurdle.