‘Now if that should be the reason in this case,’ Alleyn continued, ‘it is only a matter of time before we arrive at the truth. If, to put it plainly, Legge has been in prison, we shall very soon trace his record. But we may have to arrest him for manslaughter to do it.’

‘All this,’ exclaimed Miss Darragh with spirit, ‘all this to prove he didn’t kill Watchman. All this disgrace and trouble! And who’s to pay the cost of ut? ‘Twould ruin him entirely.’

‘Then he would be well advised to make a clean breast and tell us of his record, before we find it out for ourselves.’

‘How do you know that he has a record?’

‘I think,’ said Alleyn, ‘I must tell you that I was underneath the south jetty at six o’clock this morning.’

She opened her eyes very wide indeed, stared at him, clapped her fat little hands together, and broke into a shrill cackle of laughter.

‘Ah, what an old fule you’ve made of me,’ said Miss Darragh.

III

But although she took Alleyn’s disclosure in good part she still made no admissions. She was amused and interested in his exploit of the morning, didn’t in the least resent it, and exclaimed repeatedly that it was no use trying to keep out of his clutches. But she did elude him, nevertheless, and he began to see her as a particularly slippery pippin, bobbing out of reach whenever he made bite at it.

Alleyn was on difficult ground and knew it. The notes that he and Fox had made of the conversation on the jetty were full of gaps and, though they pointed in one direction, contained nothing conclusive.

Detective officers are circumscribed by rules which, in more than one case, are open to several interpretations. It is impossible to define exactly the degrees of pressure in questions put by the detective. Every time an important case crops up he is likely enough to take risks. If he is lucky his departure from rule of thumb comes off, but at the end of every case, like a warning bogey, stands the figure of defending counsel, ready to pounce on any irregularity and shake it angrily before the jury.

Miss Darragh had not denied the suggestion that Legge had a police record, and Alleyn decided to take it as a matter of course that such a record existed and that she knew about it.

He said, ‘It’s charming of you to let me down so lightly.’

‘For what, me dear man?’

‘Why, for lying on my back in a wet dinghy and listening to your conversation.’

‘Isn’t it your job? Why should I be annoyed? I’m only afraid you’ve misinterpreted whatever you heard.’

‘Then,’ said Alleyn, ‘I shall tell you how I have interpreted it, and you will correct me if I am wrong.’

‘So you say,’ said Miss Darragh good-humouredly.