He riffled through the pages. The book had been published in 1929 and appeared to be a series of short and pleasantly written essays on the behaviour and eccentricities of freshwater fish. It contained an odd mixture of folkishness, natural history, mild flights of fancy and, apparently, a certain amount of scientific fact. It was illustrated, rather charmingly, with marginal drawings. Alleyn turned back to the title page and found that they were by Geoffrey Syce: another instance, he thought, of the way the people of Swevenings stick together and he wondered if, twenty-six years ago, the Colonel in his regiment, and the Commander in his ship had written to each other about the scaly breed and about how they should fashion their book. His eye fell on a page heading, ‘No Two Alike,’ and with astonishment he saw what at first he took to be a familiar enough kind of diagram … that of two magnified fingerprints, showing the essential dissimilarities. At first glance they might have been lifted from a manual on criminal investigation. When, however, he looked more closely, he found, written underneath: ‘Microphotographs. Fig. 1, Scale of brown trout. 6 years. 2½ lbs. Chyne river. Showing 4 years poor growth followed by two years vigorous growth. Fig. 2, Scale of trout. 4 years. 1½ lbs. Chyne river. Note, differences in circuli, winter bands and spawning marks.’ With sharpened interest he began to read the accompanying letterpress:

‘It is not perhaps generally known,’ the Colonel had written, ‘that the scales of no two trout are alike: I mean, microscopically alike in the sense that no two sets of fingerprints correspond. It is amusing to reflect that in the watery world a rogue-trout may leave incriminating evidence behind him in the form of what might be called scales of justice.’

For the margin Commander Syce had made a facetious picture of a roach with meerschaum and deerstalker hat examining through a lens the scales of a very tough-looking trout.

Alleyn had time to reread the page. He turned back to the frontispiece – a drawing of the Colonel himself. Alleyn found in the face a dual suggestion of soldier and diplomat superimposed, he fancied, on something that was pure countryman. ‘A nice chap, he looks. I wonder if it would have amused him to know that he himself has put into my hands the prize piece of information received.’

He replaced the book and turned to the desk with its indescribable litter of pamphlets, brochures, unopened and opened letters, newspapers and magazines. Having inspected the surface he began, gingerly, to disturb the top layer and in a moment or two had disclosed a letter addressed to ‘Octavius Phinn, Esq,’ in the beautiful and unmistakable handwriting of Colonel Cartarette.

Alleyn had just had time enough to discover that it contained about thirty pages of typescript marked on the outside: ‘7,’ when he heard Fox’s voice on the stairs. He turned away and placed himself in front of the portrait.

Mr Phinn and Fox reappeared with the fishing gear.