Assassin's Vow

"Her first vow was “I do.” Her second vow was to hunt down her husband’s killer. Rachel Jaeger planned to become a linguist, not an assassin, but it works for her. For the first time in her life, she has true love, meaningful work, and a bright future.
That bright future explodes when her husband is captured on a mission. Heartbroken and lost, Rachel throws herself into her work, becoming the angel of Death to those unlucky enough to cross her path. Finally, Rachel has a chance to go after her husband’s killer. But first she must face a much more formidable opponent. Herself."