The Obscure Duchess of Godwin Hall by Hanna Hamilton

When the late Duke of Leinster suddenly dies, Rebecca Winterson finds herself trapped in the most terrible marriage of convenience with the most unsuitable partner she could have ever hoped for – her unpleasant and egocentric childhood friend and now the new Duke, Charles Godwin. Not only does she see him as a friend but she is also madly in love with his brother Andrew who, torn between duty and the strongest feelings of love for his dazzling friend Rebecca, watches his life quickly fall apart. But when an unexpected tragedy hits Godwin Hall and all intentions are being questioned, the manor’s inhabitants will have to face a vicious murderer on the loose and a secret that drives them all into darker realms.