Given the following context:

A woman's mistakes come back to haunt her in a terrifying and very literal manner in this mind-bending thriller. Dr. Samantha Goodman is a clinical psychiatrist who works with patients at an institution for the criminally insane. Things have not been rosy for Sam lately—she's been violently attacked by one of her patients, her marriage to husband David is in bad shape, and she has an inoperable brain tumor that's growing at an alarming rate.
Sam needs a weekend away from the city, but what David has set up isn't especially relaxing for her—a short holiday at a remote cabin, where David will be editing his latest book with the help of Sam's younger, attractive sister Melody. As Sam watches sparks begin to fly between her sister and her husband, Harlan Pyne and his friend Adrian break into the cabin and announce their presence by shooting Sam's pet dog.
Harlan is a convicted sex offender and murderer who was placed under Sam's care in the institution and wasn't happy with the experimental treatment he received; having escaped, he and Adrian have tracked her down and decide to take revenge by forcing Sam, Melody, and David to participate in a series of strange and humiliating games.
The Dark Hours was the first feature-length film from director Paul Fox, who subsequently directed the Douglas Coupland scripted comedy, Everything's Gone Green, as well as a number of successful Canadian television series.

answer the following question:

Who is the sister of the doctor that the sex offender takes revenge on? 

Melody