When her partner lost his leather-bound vintage Hermès diary, Brigitte Benkemoun, a journalist in France, helped him find a replacement on eBay. A few days later, the substitute diary arrived, looking much like its predecessor, only with the refill pages removed. Closer inspection revealed a crucial difference. Tucked inside the interior pocket were a slim address book and calendar for the year 1952. As Benkemoun slipped the forgotten papers free, her eyes lit up. Here, scrawled across twenty pages, were the addresses of, to name just a few, Balthus, Braque, Brassaï, Chagall, Cocteau and Lacan. Someone extraordinary must have owned this book. The question was, who?

Benkemoun made various enquiries, tracking down the vendor and the auction house that had handled the diary’s sale, but the trail ran cold. Although the handwriting was difficult to decipher, she guessed that it had belonged to a woman – an artist, to judge by the number of gallery contacts