Into Temptation by Penny Vincenzi

The Lytton family past is full of secrets, and only Lady Celia knows them all. There's her daughter Adele's difficult, dark past; the dreadful cruelty of a truth her son Kit had to confront; even the shadows of Celia's own life, and that of Barty Miller, the child she rescued from the slums in babyhood and who now owns more than half of the Lytton publishing house. Some secrets are more dangerous than others, some shared with Celia's family, some entirely her own. And all absolutely safe in her keeping. Until something happens that threatens to reveal them all ...