S4·E10 When Darkness Falls

Sam agrees to do a favor for a friend by looking into the identity of a young amnesiac who was found wearing expensive clothes by two police officers. The investigation leads them to a play the woman was involved in and a mugging gone wrong, then they follow the trail to the woman's past, which seems to have been the trigger for her amnesia. Jack takes some time off work to deal with his father, who is getting worse as his Alzheimers begins to take over and his kidneys fail. Jack finally convinces Frank to seek help, but it's too late, and Jack has to say goodbye to his father.