`All right. Here she goes.'
Mrs Larkin's manner underwent a subtle change. That afternoon she had seemed all tight corsets and severe tailoring, like an especially forbidding schoolmistress. Now the stiffness disappeared into an easier slouch and she dropped into a chair.
`What we want to know is everything you did to-day, Mrs Larkin,' Hadley told her.
`Well, in my profession a man we always look for is the postman. I was up early, ready for him. He always puts the letters in the box of Number 1, my place, first, and then goes across the way. I can time it so that I'm picking up the milk bottle outside my door when he gets out the mail for Number 2. And that was easy. Because X19 — that's the way we have to describe people in the confidential reports — X19 always wrote her letters on a sort of pink-purplish kind of paper you could see a mile off.'
`How did you know,' inquired Hadley, `that the letters were from X19?'
She looked at him. `Don't be funny,' said Mrs,Larkin, coldly. `It's not healthy, for a respectable widow to get into people's flats with a duplicate key. And it's a damn sight less healthy to be found steaming open people's letters. Let's say I overheard them talking about the first letter she wrote him.
`All right. I'd been warned X19 was coming back to London Sunday night, and so I had my eyes open this morning. I was kind of surprised when I went out to pick up my milk bottle and found Driscoll picking up his milk bottle just over the way. He never gets up before noon. He had his door open, and I could see the inside of the letter-box.
`He stuck his hand in the letter-box, pulled out the pink letter, and sort of grunted, and put it in his pocket without opening it. Then he saw me, and let the door slam.
'So I thought, "What ho!" And I knew there was going to be a meeting somewhere. But I wasn't to watch him. I'd only been planted opposite so I could catch X19 with the goods.'
`You have been a long time in doing it,' said Hadley.