The Son's Secret by Daryl Wood Gerber

University dean Maggie Lawson is struggling to repair her relationship with her son Aiden. Divorcing his cheating father, Josh, didn't help. Neither did Aiden's all-too-sudden rebound marriage. So when Aiden is slow to text back, Maggie give him space. Until Josh is shot...and suddenly, Aiden isn't responding at all. Maggie knows something is terribly wrong.