Don't Let It Show (Undercover Intrigue #1)
Tess St. John

Undercover FBI agent Sam Newton is in Houston to catch drug dealing cops while pretending to be one. His identity must be kept top secret, but his attraction to Gail can't be concealed or ignored. He's tried, repeatedly.
As their love deepens, Gail confides she doesn't believe the man in jail for her mother's murder is guilty. She and Sam investigate her mother's case, hitting nothing but dead ends. When tragedy strikes, Gail is left with only the email riddle, which leads her on a deadly quest for the truth about her mother's life and death;if she can stay alive long enough to solve it.