The Olympic Games may never have opened so beautifully as they did last night. But however stupendously you dress it, a nightmare is still a nightmare

The 28th Olympics of the modern era could, when all the bills are in, cost Greece as much as £6bn ­ or 2 per cent of the national product ­ and much of it has literally gone into the sky with a round-the-clock Awacs patrol and the greatest peacetime security shield the world has seen for a single event.

But, in the past 24 hours, there has been another kind of accountancy and when it is finished, in two weeks' time, there is the growing possibility of a crushing conclusion. It may be that the world will agree with the downcast Greeks whose joy at their organisational triumph in the face of widespread scepticism fell like a stone thrown from Mount Olympus when they heard their most celebrated sportsman and woman had fled from dope testers on Thursday.

Konstadinos Kederis, who won gold in the 200 metres in Sydney four years ago, and Ekaterina Thanou, silver-medallist in the 100 metres, spent yesterday in hospital nursing injuries from a motorcycle accident that allegedly occurred only after the Olympic authorities had been informed they had left the athletes' village just before a scheduled test.

The world may say the Olympics have run too long and with too much corruption, too many lies, and that, finally, their time has passed.

It is not a new threat, the Greek heavens that were illuminated so brilliantly here in the opening ceremony know well enough. Every Olympics since Seoul in 1988, when the 100 metres champion Ben Johnson was stripped of his gold medal, have been disfigured by drug scandals but the one that exploded here in the faces of the Athens organiser Gianna Angelopoulos and Olympic chief Jacques Rogge carried a specially devastating force. Shatteringly, it came on the eve of that point where the Olympic movement every four years talks of renewal and hope and the invigoration of the world's youth ­ and it struck down the host nation who have spent so much and on whose enthusiasm the spirit and mood of the Games always depend.

Of course, there will be moments of diverting spectacle ... and perhaps even unforgettable drama. Tomorrow Britain's superb yachtsman Ben Ainslie will start his campaign to win a third Olympic medal in the capricious winds of the Saronic Gulf. On Monday, Australia's Ian Thorpe competes against the American wunderkind Michael Phelps in the Olympic pool in a duel billed as the race of the century. Paula Radcliffe, who campaigned so ferociously against drug cheats, is one of the favourites to lead the field into the 1896 Olympic Stadium at the end of the marathon.

But all of that will happen under the terrible shadow of Greece's bone-deep grief that its great adventure has been so desperately compromised by Kederis and Thanou ­ the man and the woman on whom the nation's greatest hopes had rested most heavily.

The reaction to the accident, which forced a delay in an urgent disciplinary meeting empowered to ban Kederis and Thanou for two years, is one of scepticism. For the missed drugs test ­ the athletes are said to have missed another test when they left their US training a day early ­ there is only a mixture of shock and disbelief.

On the streets of Athens yesterday, it was as though the light in thousands of eyes had been switched off. Andreas Katsaros, 23, an Olympic volunteer and former runner who will soon start PhD studies at London University, said: "This affects me in my heart but I'm sure it will not worry sponsors like Coca-Cola too much. I'm working for the Olympics because I'm proud of my country and I want to help but the truth is I don't believe in these Games. I don't believe that as a runner you can win an Olympic title without taking drugs ­ so what do we have? Just a big lie. It is terribly sad."

The embattled Olympic chief Mr Rogge, a Belgian lawyer, insists that the Games are bigger than any individual frailty, and that the battle against drugs will be waged until it is won. He says that when Kederis and Thanou face Olympic justice ­ probably on Monday morning ­ there will be no cover-ups or evasion.

It is a familiar declaration and no doubt Mr Rogge is hoping the drama of the weeks ahead will push Greek tragedy into the margins. A race of the century or some other astounding performance might reinstate the motif of a winning laurel crown rather than a golden syringe.

That is the old hope of an Olympic apologist but, even as the sky was lit with beauty last night, it had never seemed so fragile. This, you have to fear, is a nightmare that will never go away.