Death At Blenheim Palace

Description for DEATH AT BLENHEIM PALACE by Robin Paige:

The ancient park surrounding what is now Blenheim Palace is said to be the place where Henry II carried on his liaison with Rosamund--who perished, many suspect, at the hands of Eleanor of Aquitaine. Now, as Charles and Kate Sheridan arrive in 1903, at the invitation of the Duke and Duchess of Marlborough, it is the site of a new mystery.

As Kate labors on a book about the legendary love affair, she is distracted by the disappearance of a household maid--and Charles discovers that a mysterious woman seems to be offering the famous Marlborough Gems for sale. Then the duke and his teenaged mistress vanish--and soon Winston Churchill and the young T. E. Lawrence make appearances as intrigue, and history, repeat themselves...

This is #12 in An Edwardian Mystery.