The Locked Ward, the memoirs of a psychiatric orderly working in a Scottish hospital, might have been one kind of book, but ends up being another.

It might have been the kind of book that tried to tell us where we're going wrong in our treatment of patients with mental health problems; it might have prescribed a solution.

It might also – because the author Dennis O'Donnell is a student of English literature – have been the kind of book that tried to put right what novels have done to our view of insanity. It might have tried to banish the image of the first Mrs Rochester starting fires in Jane Eyre, or Renfield biting down on an insect in Dracula, or Patrick McMurphy staring into space after his lobotomy in One Flew Over The Cuckoo's Nest. Those images are old ones. But they stick.

However, The Locked Ward ends up being none of those books – it doesn't analyse or proselytise; it just relates what happens in a ward in vivid, bloody, scatological detail. It is not a solution or an answer; it is a despatch, a factual account, a news report from a zone we rarely hear from.

In the middle of that zone are patients like Johnny. O'Donnell remembers how Johnny would pace up and down the ward then suddenly stop and ask if he was on the right road for the bus stop. Later O'Donnell would find him slumped in a chair, cap and jacket still on, sound asleep. "And my throat would close a little," says O'Donnell. "He reminded me of my grandfather."

The most moving section of the book, however, is when O'Donnell describes the effects of mental ill health and, in particular, dementia; he talks about the pinboards at the patients' bedsides covered in pictures of friends and relatives. Those pictures were, he says, like stills from movies but movies nobody could remember.

Equally moving is the section where O'Donnell describes what dementia does: "The days get pared away from the memory, and then the months and the years, but from the wrong direction. It happens backwards. Finally, the memory is erased - Each day was their first day. And they would never escape, never get better."

If there is a fatalistic tone to this description, it's because there is a fatalistic tone to the book. O'Donnell describes what conditions are like in a locked ward – long stretches of boredom with flashes of violence – and seems to accept it will always be so.

He also appears to take a similar approach to the subject of whether some wards should be locked in the first place. He acknowledges how awful it can be to be contained and quotes Blake: "A robin red breast in a cage/ Puts all Heaven in a rage." He also admits that, in many cases, locking a patient up increases the likelihood of aggression. If this is just a prison under another name, then it will have the same effects as a prison – the inmates will become depersonalised, stigmatised, resentful, mutinous, violent. And yet, in the end, O'Donnell seems fatalistic about all of this too: some wards must be locked because there will always be some patients who need to be locked up.

What does feel odd though is that O'Donnell does not go further and give us more of his views on the treatments he witnessed and sometimes imposed. For long stretches of the book, it feels frustrating that the patients come in, tell their stories and then go out again, and we get no sense of how they get on, or if they are cured or helped. Until you realise O'Donnell is only reflecting what it was really like in the hospital: patients do disappear and the staff often don't know what happens to them.

And that's when O'Donnell does, finally, attempt to refute those old novels with their garish, ghoulish representations of mental health. In a real ward, he says, there are no fictional narratives, no cinematic happy endings, just life as it is.

The Locked Ward

Dennis O'Donnell

Jonathan Cape, £16.99