Last Night's TV - Father & Son, ITV1; Nixon in the Den, BBC4

Jesus, break my fall," muttered Michael O'Connor in the final frame of last night's episode of Father & Son. We might still be in doubt about whether Mikey – former Manchester ganglord – is going to hit rock bottom, but he already seems to know there is no alternative. And if you fret at the sacramental overtones here, you can hardly say you weren't warned. Frank Deasy's thriller, running over four consecutive nights on ITV1, begins with Johnny Cash singing "God's Gonna Cut You Down" and rarely wastes an opportunity to slip in a close-up of a bible or a crucifix. It's very first word – murmured over the modern nativity of an ultrasound Polaroid – was "Miracle" and what followed was a tale of sin and redemption and blood sacrifice, a variation, for Deasy, on his last big drama for the small screen – The Passion, an HBO mini-series about Jesus's last week on Earth.

Father & Son is Deasy's last big drama in a different sense. He died last year, unexpectedly, though perhaps not entirely unpredictably, during transplant surgery forced on him by liver cancer. That's a fact that gives a certain edge to one of his plot strands – the desperation of a long-term convict dying of kidney disease and planning to break out so that he can buy some new ones in China. But it also makes criticism trickier than it might usually be. There isn't going to be another chance for him to get it right. It's a relief, then, to say that, while Father & Son isn't perfect, its virtues are more than enough to make you forgive its small failings.

It began terrifically, with an entirely novel addition to the repertoire of cinema's ominous noises – the rubbery zip of BMX tyres over tarmac as two hoodied riders race towards a killing. A young boy was shot in the street and Sean O'Connor – studious, innocent, God-fearing – found himself inextricably tangled in a gang feud between the Motorway Crew and Young South. And when the police turned up, he was the one holding the gun over a dying boy, out of misplaced loyalty to a girl he thinks is his friend. This looked like an accident but wasn't, having been contrived by Barrington (the one dying of kidney disease) to lure Sean's father out of retirement. And Michael – on the brink of being a father again with a new young wife in Ireland – couldn't resist the lure, hoping that he could now make good parental failures in the past.

That was one of the virtues, the way that Deasy has constructed a set of interlocking circumstances that appear to give his characters no good choices. Sean can tell the truth about who pulled the trigger, but then he'll be killed for grassing, rather than for revenge. Sean's police officer aunt, played by Sophie Okonedo, can stay clear of the case for professional reasons, but if so she won't be able to prevent the destruction of every hope she'd had for him. And Michael's wife finds herself torn between repulsion for the kind of things he's now going to have to do and a desire to help him do them so that they're finished with quicker. And while all of these circumstances might raise the odd quibble about plausibility (would a police officer really live on a street so hostile to police officers?) they knit together into something gripping.

Last night, Deasy turned the screws even tighter, and included a heart-stopping scene that hinted at how the pollution of gang and gun culture spreads everywhere. When the police raided the home of the boy who had been killed – hoping to forestall a revenge shooting – his younger brother smuggled the gun out of the house in his school-bag and later drew it on Sean's sister in his primary school class, the imperative to return fire already absorbed. And since we as viewers were still unsure how far the drama was prepared to go to shock us, there was the horrible possibility that he might actually pull the trigger. We were spared that, I'm glad to say, and Michael's concluding prayer was offered up just after another small mercy – his decision not to kill the teenager who'd been tracking him with a gun but to chase him out of town instead. Britain's Got Talent may have ended, but this dark, serious, thoughtful thriller is a much better way of making the same point... and about Ireland too, obviously.

Nixon's last term was as close as politics get to a noir thriller – small sins snowballing into big ones, enemies closing in and the man at the heart of it desperately looking for some way out. David Reynolds recap of the basic narrative in will only have been revelatory to those too young to sit up till after midnight for the nightly thrill of the Watergate hearings. But he told the story well – and his regrettable weakness for doing all the voices didn't get too far out of hand, barring a moment at which he alternated between an impression of Nixon and Leonid Brezhnev. And, since the issue of plausibility came up earlier, who would have believed Nixon's first address to the American public about the Watergate break-in, if a scriptwriter had invented it? "What really hurts with these things," he said in his broadcast, voice trembling with sincerity, "is if you try to cover it up." Come on... there's no way that nemesis could be that neatly foreshadowed, surely.