On 15 July 1942, Rayski was returning to the room he rented in Paris under a pseudonym together with false papers that declared him to an Aryan, unaware that his wife was trying to flee Paris that day with their son. As a "résistant", Rayski felt it better to live apart from his wife. On that day, he recalled that his major concern was the unpleasant smell in the summer heat caused by the sauerkraut that German soldiers were always eating in the outdoor restaurants of Paris. At about 4: 30 am on 16 July about 4, 500 French policemen began an operation known as the Vel' d'Hiv Roundup to arrest every single Jew living in Paris. On the morning of that day, Rayski described the scene he saw as he entering the Paris Metro: "I was descending the stairway leading to the quasis, when I saw before me, buses turning in the direction of the Grenelle bridge, today the Bir-Hakeim bridge. Their unusual appearance struck me instantly. On their back platforms, you could see policemen surrounded with packages, suitcases and all sorts of bundles...Before crossing the bridge, the buses slowed down and I could see some faces. No more possible doubt, simply from the grief of their expressions, I knew what was going on. My knees buckled under my body, I had to lean against the rail. The comrade I met at the meeting place confirmed it. "Yes, it is a massive round-up"". Rayski spent all of that day, known in French history as Black Thursday, trying to contact his wife to see if she and their son had had escaped. Rayski was greatly relieved to find that both his wife and his son had escaped the "grande rafle" (great round-up) of 16-17 July 1942. After hiding their son away with a teacher friend of his wife, Rayski spent the night with his wife at his room, where he noted that she was shaken by the "grande rafle" that she had might difficulty sleeping and held him tight, saying she was so afraid that he had been lost that day.