“Life’s not just a bag of shit, but a leaky one. You can’t help but be touched by it,” says Benedict Cumberbatch’s titular feckless aristocrat in Patrick Melrose. But Patrick is not just touched by it, he’s up to his neck in the stuff.

This five-part adaptation of the autobiographical novel series by Edward St Aubyn has been an electrifying portrait of a man paralysed by trauma while trying to be better than the wretched beings who raised him. When he learns of the death of his father, we watch as his knees buckle, but not through grief – Patrick is reaching for a dropped syringe. For him, a death in the family sits comparatively low in the list of life’s catastrophes, which have included sexual abuse, neglect and a monstrous heroin and cocaine habit. The opening episode, which reversed the order of the first two books, was a magnificent display of train-wreck debauchery, with Patrick forcing grubby needles into resistant veins, clumsily attempting suicide and crawling pitifully along the marble floors of his luxury New York hotel before flying home, his father’s ashes in hand, in a haze of shivering withdrawal.

Viewers imagining further scenes of depravity have been happily wrong-footed in subsequent episodes that – in shifting between different periods – have yielded startling changes in tone and pace. In the last few weeks, we have moved from a sun-dappled chateau in the south of France in the 70s, where the horror of Patrick’s childhood is revealed, to the English country pile of Lord and Lady Gravesend 20 years later, then back again to France in the early 2000s where Patrick, now a father of two, is engaged in a daily battle to not behave like a dickhead.

In the final act, Patrick is once again plunged into the past as old ghosts gather. That the series doesn’t deliver a straightforward redemption narrative is one of its triumphs. For all of Patrick’s idle privilege, manifest here in the sumptuous scenery and endlessly fabulous outfits, his pain is too complicated, his wounds too deep, to allow him to function as a regular human. “This is rage, my heart is racing with it,” he roars at his wife, who mistakes his tears for grief.

There are, of course, scores more lost souls here, from Patrick’s mother (Jennifer Jason Leigh), a brittle heiress who dashes off cheques to Save the Children as her eight-year-old son silently pleads for mercy, to his malevolent, manipulative father (Hugo Weaving), for whom life is about satisfying his needs above all others.

And there’s the ever-present family friend, Nicholas (Pip Torrens), a grim emblem of British upper-class disdain. Privy to the source of Patrick’s pain, he nonetheless delivers a stinging soliloquy on “this degenerate age of confession and complaint, when Freudian mumbo-jumbo is emptied on to every conversation like vinegar on to a newspaper full of sodden chips”.

Patrick Melrose is a sensational saga, buoyed by exceptional performances and note-perfect writing. It shows how our past shapes our present and charts the corrupting power of wealth and privilege. Life is a bag of shit, even when you’re rolling in it.

Sunday, 9pm, Sky Atlantic