Fatal Sisters — Leon Shure

The first in the North Shore Mysteries series: When her husband's mistress, Megan Spevak, is murdered, Ashleigh Simon must flee her pleasant suburban life and take Megan's place in the city or be murdered herself. A good plan until Megan's brother, Tommy Spevak, returns from military service and finds his sister has been replaced by an imposter. Hoping to find out what happened to his sister, Tommy hides his own identity and fakes a friendship with the woman who he calls Meg. But when Tommy starts to fall in love with Meg, he discovers that both are now being stalked by Megan's murderer.