That must be the true terror, surely. Not to be totally lost in a fugue state, held in that tranquil suspension where such people go when they forget themselves. But to flick in and out, to be one minute all there, and one minute gone, the former judging the latter brutally and in despair.

So it was with Kurt Wallander (BBC1) whose distress at the impact of his early onset Alzheimer's was beautifully and painfully captured by Kenneth Branagh in the last ever of the series of the downbeat Swedish-set drama.

There were two of them now – the sharp humane detective, and the stranger who randomly stole his faculties and replaced them with anxieties and humiliations.

“Sometimes I find I can’t even imagine where I’m supposed to be,” he said. “You hit a wall. You try and go over it, round it, some other way. You get so anxious, get angry. I try and think back to things that must have happened and it’s just the pictures aren’t there any more. It’s like they’re dissolving.”

Read more In The Catch, love is the biggest con of them all

Meanwhile he is exploring the murky background of his daughter’s father-in-law Haken who has gone missing, prompting the apparent suicide of his wife Louise. Haken might have been involved in a cover-up of Russian submarine activity years ago which a historian is hungry to explore and expose. But that simple explanation could be a veneer for an altogether darker reality of treachery and double-dealing.

It is a complex problem, across two time frames, mingling Wallander’s professional duties and familial loyalties.

Kenneth Branagh as Kurt Wallander

Balancing these challenges is the meat of Wallander’s professional life, but not that of his capricious mental invader who has trouble forming sentences and sends him careering around a field clawing at his clothes.

So he does what a proud, self-aware man must do to maintain his reality. He writes himself notes, recites names and numbers in the shaving glass, gives himself breadcrumb clues so he can find his way back from the dizzying maze. But no trick is adequate. The pretence will burn through the facade eventually.

“Being a parent is a long process of letting go,” he tells his son-in-law. Being a person also, one supposes.

He holds a sugar cube half in his coffee, the brown liquid invading the crystals; it crumbles in his fingers.

“It’s moments now. My life doesn’t join up,” he tells the apparition of his father on the beach.

And a good man is lost.

Follow The Wharf on Twitter @the_wharf .

Keep up to date with all our articles on Facebook .