‘But why should he think the letter would be here? He’d know I should have it on me or else have passed it on.’

‘Begging your pardon, sir, that’s just what he wouldn’t know. He may have tumbled to the fact that you’re not the original Mr Blunt, but he probably thinks that you’re a bona fide gentleman who’s bought the business. In that case, the letter would be all in the way of regular business and would be filed as such.’

‘I see,’ said Tuppence.

‘And that’s just what we’ve got to let him think. We’ll catch him red-handed here tonight.’

‘So that’s the plan, is it?’

‘Yes. It’s the chance of a lifetime. Now, let me see, what’s the time? Six o’clock. What time do you usually leave here, sir?’

‘About six.’

‘You must seem to leave the place as usual. Actually we’ll sneak back to it as soon as possible. I don’t believe they’ll come here till about eleven, but of course they might. If you’ll excuse me, I’ll just go and take a look round outside and see if I can make out anyone watching the place.’

Dymchurch departed, and Tommy began an argument with Tuppence.

It lasted some time and was heated and acrimonious. In the end Tuppence suddenly capitulated.

‘All right,’ she said. ‘I give in. I’ll go home and sit there like a good little girl whilst you tackle crooks and hobnob with detectives—but you wait, young man. I’ll be even with you yet for keeping me out of the fun.’

Dymchurch returned at that moment.

‘Coast seems clear enough,’ he said. ‘But you can’t tell. Better seem to leave in the usual manner. They won’t go on watching the place once you’ve gone.’

Tommy called Albert and gave him instructions to lock up.

Then the four of them made their way to the garage near by where the car was usually left. Tuppence drove and Albert sat beside her. Tommy and the detective sat behind.

Presently they were held up by a block in the traffic. Tuppence looked over her shoulder and nodded. Tommy and the detective opened the right hand door and stepped out into the middle of Oxford Street. In a minute or two Tuppence drove on.

‘Better not go in just yet,’ said Dymchurch as he and Tommy hurried into Haleham Street. ‘You’ve got the key all right?’

Tommy nodded.

‘Then what about a bite of dinner? It’s early, but there’s a little place here right opposite. We’ll get a table by the window, so that we can watch the place all the time.’