‘I notice you do crosswords, Mrs Gallagher.’

She glanced up at him, startled by this twist in the conversation. ‘What?’

He motioned with the paper. ‘I like crosswords myself. That’s why I was interested when I saw you’d completed today’s puzzle. Very impressive. When did you do that?’

‘This morning,’ she said through another handkerchief. ‘In the park. I always do the crossword after I’ve bought the paper. Then I bring it home so George can look at his horses.’

Rebus nodded, and studied the crossword again. ‘You must have been preoccupied with something this morning then,’ he said.

‘What do you mean?’

‘It’s quite an easy one, really. I mean, easy for someone who does crosswords like this and finishes them. Where is it now?’ Rebus seemed to be searching the grid. ‘Yes,’ he said. ‘Nineteen across. You’ve got the down solutions, so that means the answer to nineteen across must be something R something P. Now, what’s the clue?’ He looked for it, found it. ‘Here it is, Mrs Gallagher. “Perhaps deadly in part.” Four letters. Something R something P. Something deadly. Or deadly in part. And you’ve put TRIP. ‘What were you thinking about, I wonder? I mean, when you wrote that? I wonder what your mind was on?’

‘But it’s the right answer,’ said Grace Gallagher, her face creasing in puzzlement. Rebus was shaking his head.

‘No,’ he said. ‘I don’t think so. I think the “in part” means the letters of “part” make up the word you want. The answer’s TRAP, Mrs Gallagher. “Perhaps deadly in part”: TRAP. Do you see? But you were thinking of something else when you filled in the answer. You were thinking about how if your husband tripped down the stairs you might be rid of him. Isn’t that right, Grace?’