Guarding the Countess by Jess Michaels

Naomi Barnaby’s husband, the Earl of Walridge, just died under mysterious circumstances. Her third husband to do so in just a handful of years. She wants to know if the men in her life were murdered and hires investigators Captain Marcus Ridgeway and Everett Bryant, Marquis of Glenmarrow to look into the matter.
When the alluring Naomi is attacked in their driveway, Marcus and Everett decide to take a far more personal interest in protecting her and uncovering who killed the men in her life. Soon the three are involved in an intense affair that challenges feelings between each member of their triad.
But the shared history between Marcus and Everett is something that cannot be ignored. And those threatening Naomi may destroy everything the three could mean to each other and the unique future they long to build.