TELEVISION / When did you last see my father?: Thomas Sutcliffe on a triumph of experience over hope

WHEN IT was suggested to Colonel John Robertson that he might fly a desk through the Vietnam war he wrote a 17-page letter to his superiors arguing that he should be allowed to pilot something a little more dangerous. On the evidence of True Stories (C4) his daughter appears to have inherited both his tenacity and devotion to duty. Despite the fact that she could run her finger over Robertson's name on the granite wall recording America's war dead (he was declared Missing in Action after being shot down over hostile territory) she was convinced that he was still alive. True Stories followed her to Moscow, Phnom Penh and Saigon as she attempted to weld a cast-iron case out of clutched straws.

Her conviction began with a photograph, apparently showing her father and two other missing airmen in the Cambodian jungle. To the casual eye the match looked good, the clean-cut snapshot of a young flyer fading smoothly into the coarser, older face in the new picture. But the Pentagon insisted that it was a hoax, a crudely altered picture of Soviet farmers taken from a propaganda magazine distributed in Cambodia. Where the match with the American flyers had been persuasive that with the Soviet magazine was perfect.

Provided, that is, that you looked with indifferent eyes. In an extraordinary demonstration of the limitless cunning of hope Deborah Robertson took the view that the Pentagon had faked the original magazine. Computers were used to prove that a smudge on the original matched a mole on John Robertson's neck, despite the fact that his Soviet doppelganger was clearly wearing a high collar. Responding to the Rorschach blot of the blurry enlargements, Deborah Robertson revealed an unhealed wound of grief.

From then on it was a narrative of disappointments and failed hope, though no less gripping for that. In Moscow, where she hoped to prove that the Soviet magazine had never existed, Robertson discovered that Novosti had the original photograph in their archives, dated from 1939. In Phnom Penh verbal reports of sightings proved confused and unverifiable. The government office set up to look into reports of prisoners was intent on discouragement, and Cambodian contacts asked for money and offered only cruelly empty assurances rather than real proof. In Saigon Robertson entered a Graham Greene world of fixers and go-betweens, negotiating through an American businessmen (Robert Mitchum in one of his sleazier roles) to be taken to meet with her father, supposedly being held by bandits.

It didn't happen, and you would have been astonished if it had. But as it dawned on Robertson that she was being used (to what end and by whom is still a mystery) you realised that what had looked at first like an undesirable credulity was actually more valuable and that it was a real sadness to see it flicker out like this in the murky air of exploitation and lies.