The vital thing to be said about Max Pemberton's Trust Me, I'm a (Junior) Doctor is that it is not what it claims to be. Consider the cover: an illustration of a hapless blond medic clutching his stethoscope, Disney eyes, lips parted. Perhaps he's just taken someone's pulse and she's pinched his bottom. This is not Max Pemberton - not even close. The author of this book is an infinitely paler, less finished character.

Trust Me . . . is Pemberton's diary of his year as a junior doctor in a sprawling, unnamed urban hospital. He shares a flat with his fellow trainee Ruby, and struggles to enjoy his job or find the time to eat or think. Pemberton is persecuted by his pager, which bleeps continually, dragging him out of sleep and away from longed-for sandwiches, propelling him from one ward to another to dole out paracetamol and Valium, and to stand, anxiously, at the end of beds, wondering if the person in it has died or is just sulking. Death muddles Pemberton. "Rather than pronounce people dead, which to me sounds rather official," he writes, "I prefer to suggest that people have died, then leave for a bit and come back. If rigor mortis has set in, then I feel a bit more confident in my diagnosis."

The book frequently takes us out to the bins at the back of the hospital, where Pemberton sits, cigarette in hand. He worries about Ruby sleeping with her consultant (no biggie, Max - everybody does it on Grey's Anatomy). He worries about the protocol and paperwork and parking fines demanded by the hospital. There are times when you think Pemberton doesn't much like people at all. Patients in A&E are "the bawling brainless". He complains about "another weekend ruined by the ailing masses" and suggests that "children are like farts". He frowns, firmly, on those worse for wear at a party, and a great deal on Ruby's trysts: "I want to say that I told you so, to say that all this was her own fault, but what good would that do now?"

At the start of the book Pemberton cries off love and relationships, claiming a lack of time or interest. You don't believe him. Or rather, there's a bogus, story-simplifying neatness to this that will not go away. It gnaws at the reader like shoe-straps digging into the ankles. As Saul Bellow says in Augie March: "Everybody knows there is no fineness or accuracy of suppression. If you hold down one thing you hold down the adjoining . . ." We are left with the feeling that Pemberton is holding out on us in this regard and therefore, possibly, in other areas, too, not trusting us or opening his heart - essentially changing the subject, which is rather mean in a diarist.

Those of you who heard the author recently narrating extracts from this book on the radio will surely have noticed his reedy, sweet voice and wished someone in the studio had thought to give him a cushion to sit on to bring him closer to the microphone. You wish Max would turn up the volume in general - let it all hang out. Until it becomes clear that he simply cannot. In ministering to the wretched of the earth minute by minute, Pemberton has been reduced to a bleached sack. The person on the cover of this book wants to stand at the end of a bar, talking about being a doctor, wants to snog a nurse and wear a joke bow tie. The person writing this book can scarcely speak. "I could never tell them," he says, of his family, "about the horrors, about the tiredness, about the fear and uncertainty, and the feeling of responsibility that almost crush es you on a daily basis." He mentions the "dark, friendless stretches of corridor" that entwine the hospital and describes, in his very ordinary prose, desperately knocking back the protein shakes made for late-stage cancer patients, to give him strength.

The publishers, and the Daily Telegraph, for which Pemberton has written a successful column on which this book is based, think they have on their hands a kind of Tristan Farnon - the foppish, sexy vet of the James Herriot books. What they really have is a deeply melancholy and tender hero, breathing in and out misery's tides. In Trust Me . . . teenage girls are sent back out on to the streets to be greeted by their pimps, then bundled into cars. Cleaners are mugged on the way from collecting their wages with their frail hands. The once-loved and gossipy lie paralysed for weeks in their hallway before being discovered by next door's pet. Soon, they will all be hospital-bound. Meanwhile, Pemberton hovers in the background, car keys in hand, hoping to scream only part of the way home. The world pulls and tugs. He shakes.

Antonia Quirke is the author of "Madame Depardieu and the Beautiful Strangers" (HarperPerennial)