Suspicion / Leigh Russell.

"Happily married to the charismatic headmaster of a prestigious boarding school, Louise thinks her life is perfect. But after hearing that her husband is having an affair, Louise must decide how far she is prepared to go to save her marriage. Confident in her IT skills, Louise cyber bullies her rival. When the police then become involved, Louise realises she has made a dangerous choice as first one woman, then another, is found murdered. Realising she has taken on more than she intended, Louise has to make another choice, and this one could cost her not only her marriage, but also her life…"--Publisher description.