The Marquess of Temptation by Claudia Stone

Since her father’s death, Miss Hestia B. Stockbow has been living a lie. Working as a companion, under an assumed name, all she wants to do is keep her head down and forget about the scandalous tragedy that haunts her past.
There’s only one problem…
After two delicious, stolen kisses, the usually icy and aloof Alexander Delaney, Marquess of Falconbridge, finds himself entranced by Belinda Bowstock, a lowly paid companion. When he discovers that she is, in fact, his missing ward, Alex realises there’s only one thing he can do:
Marry the chit and help her solve the mystery of her father’s suspicious death.
There’s only one problem, Belinda has absolutely no desire to wed the cold Lord Delaney-and she’s not the type of lady to take orders from anyone…even a Marquess.