In season 4, Castle is contacted by a shadowy figure who says that he is a friend of Roy Montgomery and that he has been charged with protecting Beckett in his stead. Castle learns that Montgomery knew who ordered Beckett's mother's death; he had been the one who found out about the kidnappings and offered not to go to the police if Montgomery, Raglan and MacAllister gave him the money they made from the ransoms which has been estimated at several millions of dollars. According to the man, this person has grown powerful enough for the revelation to destroy him. Montgomery had kept files that, should they be revealed would harm the killer and others. The deal was that Montgomery's family and Beckett would be safe if he wanted the files kept secret. Upon his death, he had sent the files to the mysterious man and had charged him with upholding the deal. The only other condition was that Beckett couldn't go near the case or else the deal was off. Castle says that he will keep her reined in. He tells only his mother this information and confides in her as to the deal he made. Martha wants Castle to tell Beckett the truth, but Castle tells her that he can't because Beckett will be killed by the people behind her mother's murder if she keeps digging and that he has to protect her.