The staircase in Dormec House, a Ministry building, is certainly elegant, but to Arthur Timkins, messenger, one of the quota of variously disabled employees, it is the scene of an encounter that changes his life miraculously.

Selected as one of Professor Knowle's guinea-pigs in a pilot trial to enhance intelligence, he is whisked away to a world beyond his wildest dreams. Workers at Matcham Grange, from kitchen staff to the Professor himself, treat Arthur kindly.

Everything that puzzled him slowly clears, he is like a man emerging out of thick fog into sunlight. This new life comes to an abrupt end.

By the merest chance, Arthur left the Grange before the explosion that kills all his companions: his brief experience of luxury is over.

Hunted down by the spies responsible for destroying Matcham Grange, he changes identity with the tramp killed by a bullet intended for him. Grief-stricken and suffering physical hardship, he owes it to the Professor to reach the Ministry, proving there is one guinea-pig left. An outcast from society, after a hard journey, Arthur has to convince headquarters that he is the real Timkins, not a spy impersonating him.

The transformed Arthur is taken to Dormec House. The psychiatrist (who had selected him) swears that no one will recognise the down-trodden slow-witted messenger in this handsome, well-heeled executive, but someone does, on that very staircase...