Stone Cold Heart by Lisa Hughey
When Colin Davies agrees to take an off-the-books job for his old friend, billionaire Jack Stone, there's only one rule. Protect Jess, Jack's little sister, and keep his hands off. No problem. Until he meets Jack's sister and realizes it's too late. He's already had his hands all over her. Jess Stone, a former FBI sniper tired of dealing with the worst of humanity, leaves the agency determined to change her life and start working for good. On a humanitarian mission to aid an earthquake-ravaged country, finally Jess finds a purpose working for her big brother's company. The only glitch in her future plan is the appearance of Colin Davies, an operative from one of her worst cases, and a one night stand she's been unable to forget. When Jess discovers the humanitarian mission isn't the whole job, she's got a choice to make. Colin wants to protect her but she's capable of taking care of herself. Can he thaw Jess's stone cold heart?