Lolita, National Theatre: Lyttleton, London

Brian Cox was the first actor to portray Hannibal Lecter, in the movie Manhunter. He now plays another sociopath with fancy affectations as Humbert Humbert, the middle-aged émigré who conducts an abusive affair with his 12-year-old step-daughter in Nabokov's 1955 novel Lolita. There have been many earlier adaptations. Here it's filleted by Richard Nelson to create a one-man show – potentially the truest method. Narrated by Humbert in mesmerising first-person prose, the book compels and repulses as a dramatic monologue: an obsessive's warped apologia pro vita sua.

So it's sad to report that the evening (repeated over the next two Mondays at the National) is a deep disappointment. There are problems with the performance, production, editing and emphasis. A plump, pasty figure in prison pyjamas, Cox's Humbert is alone in his cell where he has just completed writing an account of his infatuation. The fact he reads to us from his notebooks (not without fluffs and stumbles) may be justified dramatically (Humbert is a vain artist manqué) but the theatrical effect is muffling. The bookish barrier stops him casting a direct, queasy spell.

It doesn't help that Cox's accent is a moveable feast, wandering from mittel-European through riffs of RP to snatches of his native Scots. He seems fundamentally miscast. The book's grotesque comedy arises from the incongruities of style and substance. An epicure of sensation, quivering with high-flown rapture at nymphets and shuddering with disgust at American vulgarity, Humbert is a persistent rapist and wilful moral philistine. But Cox's aura is more man-of-the-people than rarefied mandarin. The clash of aesthetic snobbiness and ethical squalor is muted.

Surprisingly, the emphasis is on Humbert as victim. His deviant sexuality was sealed as a teenager when his 14-year-old girlfriend died. He's undone by a culture where childhood innocence has become a myth. Cox communicates Humbert's remorse and nostalgia, but you don't need Nabokov's view of his hero – "a vain and cruel wretch who manages to appear 'touching'" – to feel the slant in this version is sentimental. It ends with Humbert declaring that through his notebooks he and Lolita will share immortality. You're in danger (as you aren't in the novel) of forgetting that no art is worth this terrible human cost.

Next performance 21 September. Box office: 020 7452 3000