ane and Maura investigate the murder of a woman killed in an arena parking garage. The dead woman had an altercation in the arena with a crazed hockey mom, Mary Bigsby, who punched her in the nose. However, she was attacked a second time in the parking garage and her throat was was slit. People remember her handing out helmet sweat pads to some of the players but the police have little else to go on. The police can't identify her or find her car in the garage. When they finally do identify her, it turns out she's a medical doctor and was seeking DNA samples from teenagers in an obvious attempt to find someone. It all has to do with the death of her sister many years ago. Meanwhile, Caitlin comes to stay with Maura for three weeks while their mother Hope has gone to Europe. Maura's not quite sure how to deal with her.

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