The walls were panelled and hung with portraits of bewigged chancellors and diplomats and there was a large and heavily decorated grandfather clock. It ticked with a constantly sticky, hesitating tick, demanding to be listened to in case it didn’t reach the next second. Wilson found the clock irritating. He wasn’t sure about Naire-Hamilton either.

‘Rome,’ announced Wilson.

‘You can’t be serious!’ Naire-Hamilton brought his hand up over his sagging eye, a habit of embarrassment.

‘I wish I weren’t.’

‘That’s… it’s…’ Naire-Hamilton’s hand moved from his eye, in a snatching gesture, as if he could pick the proper expression from the air.

‘…where the traitor is,’ said Wilson.

Naire-Hamilton carefully replaced his teacup on a wine table beside his chair and said, ‘Tell me why you’re so sure.’

‘Four months ago we started transmitting in monitored batches through normal Foreign Office channels an apparently genuine advisory document, recommending the manner of British response to Russian efforts to increase its influence throughout Africa.’

‘Why Africa?’

‘Because we had a lot of embassies to cover and the size of the continent gave us sufficient number of towns and cities.’

‘I don’t understand.’

‘The document was identical, but each message listed a different African city or town from which the intelligence prompting the cable was supposed to have come. And each receiving embassy was accorded an identifiable capital; the effect was to make each cable individual.’

‘Jolly good,’ said Naire-Hamilton. It sounded as if he were applauding the winning six during the annual Eton-Winchester cricket match.

‘Three days ago the document was relayed from Moscow to all the Warsaw Pact embassies. Our source checked back with Prague, for clarification, as we instructed. And got the reply that the message emanated from Cape Town.’