Dexter season 7

After being catched by Deb while killing Marshall, Dexter is in urgent need of at least a few convincing arguments which may explain his behavior to his sister. The only idea comes up in his mind - he pretends it was momentary insanity that pushed him to kill. Debra is shocked and confused by things she had seen and later had heard from Dexter but still accepts his defense.. although not for long. She helps him and they burn out the place of murder with any possible evidences. Later Dexter moves in Debra’s apartment. Eventually she discovers the whole truth about those "things” her brother has been doing at night for a pretty long time. But she can't betray him so she tells nothing to the police and hides all the evidences she has about his crimes. Deep in her heart she believes there are still some chances to cure him and make normal person, that’s why she keeps Dexter under her strict control. But being under such an excessive care just drives Dexter even more crazy.