‘Someone who is daltonian with regard to a colour (red or green) cannot detect its tints. The result is confusion between, for example, light red and dark yellow. It follows that if one were to draw a line composed of dots of different colours, a normal person would see just that, but a daltonian would see a straight line in a more or less homogenous tint. Obviously, if you were to write a message that way, the former would not notice it in the welter of colours, but the daltonian would see it more or less clearly.’
‘Very ingenious,’ exclaimed the Ministre de la Justice.
‘Very. For if you take the precaution of only showing the painting to people with normal vision, all they will see is a collection of harmonious colours, and nothing else. From the moment that Slowman’s intuition alerted us to the possibility of colour-blindness, we were expecting to find such coloured paintings. So, once we learnt of the existence of frescos in the Arcueil house, we were sure we were on the right track. The additional precaution of covering the paintings with wallpaper had a double objective. First of all, it prevented accidental discovery by a daltonian. Secondly, it preserved the freshness of the paint, a necessary condition for clear reading. Note that it was by an extraordinary stroke of fate that Duroyer, himself a daltonian, was charged with stripping the wallpaper and revealing the frescos. A fate which almost undid the criminal, who could scarcely have foreseen that a housepainter could be colour-blind.
‘All that, I repeat, is elementary and does not advance our enquiries. We still don’t know the essentials: what was in the message thus disseminated; and the identity of the individual responsible for this creative method of cryptography.
‘I shall start with the second question. Who could have painted the frescos? We haven’t seen them, and are relying on the testimony of young Gégène. He found a certain charm in those paintings without a subject, from which we may conclude that they were painted by a skilful artist, familiar with modern techniques.
‘I thus knew two things about our man: a painter of talent who was also familiar with the latest theories of colour-blindness. Here, I had a considerable advantage, which I don’t wish to boast about. As soon as I connected painting and colour-blindness, I remembered a student of mine some fifteen years ago who had written a remarkable thesis on the latter. His name is Bernard Argier, and he was born in Egypt, the son of a French engineer and an aristocratic Egyptian lady.’
‘What happened to this Egyptian?’
‘I’m getting there. After he passed his exams, he returned to Egypt. His father had died almost penniless a long time before, and his own health had been badly affected by the climate and pleasures of Paris. What he did there I do not know. It appears he returned to France in 1933, but I haven’t been able to trace his wanderings. Nevertheless, about two years ago, he was back in Paris. He was a veritable wreck: poor, without a job, unable to use his brilliant talents and, worst of all, afflicted with who-knows-what disease. The doctor who treated him, practically for free, could never work out what it was. Although it was basically a form of tuberculosis, there was also radiation-induced dermatitis present.
‘At the beginning of 19.., in other words, roughly eighteen months ago, Argier was hospitalised, and placed in the care of Dr. André Richard.’
The name surprised us, particularly since it appeared naturally in the professor’s account. His voice had remained steady up to that point but, with those two words, it broke. It was the only thing which revealed the emotions of the professor, and all the more poignant for that. We remained silent for a moment, without looking at the heart-broken father. When he started speaking again, the only trace of emotion was in his more rapid speech.
‘My son was interested in the sick man’s case, as much for the strangeness of his affliction as his subtle intelligence, albeit sarcastic and bitter. He kept me informed and shared his findings with me. He was never able to solve the mystery of what killed poor Bernard. He died in October, during a brief absence on the part of my son. The autopsy wasn’t able to find anything we didn’t already know.
‘I arranged to speak to my son’s favourite nurse, who had looked after Argier until the end and was with him when he expired. I thought she might have some information. Here’s what she told me. About two weeks before his death, Bernard asked that a telegramme be sent to his half-brother Arnault, demanding to see him urgently. The latter replied that he would arrive via Marseille but, being very tired, would need to stay there overnight and would not arrive in Paris until the evening of the 10th. Bernard died on the morning of the 9th. He was lucid to the last and, desperate to see his brother, he asked the nurse to convey this simple but very important message to Arnault: “Sade—Dalton—Curie”.’
The professor paused again. Emotions were running high. We sensed the end coming.
‘And did the nurse pass the message on?’ asked the Président.
‘When the telegramme announcing his brother’s death arrived at Arnault’s hotel, he himself was already dead from a heart attack. The nurse, not knowing what to do, passed the message on to my son. He promised to take care of it. But he was very busy with his research at the time, and put it off until later. I myself was away, and didn’t hear anything. As far as I know, only one of his best friends heard anything about it. I didn’t return until the end of the month, called back by an urgent telegramme... as you know....’
This time his
