The Equalizer S01E11 - Desperately

A bored housewife is dared by her friend to pick up a guy which she does. He takes her to a hotel room but when they arrive there's a guy already there. The guy who brought her there pulls out a gun and kills the man there. She runs away and calls McCall but she doesn't want her husband to know what happened. When she tells him what happened, McCall deduces that the man is a professional killer so they go to the police and she tells her husband. But the assassin tracks her down through her friend.