Alan & Katherine (S15E05)

Alan Parker's most haunting memory of his mother is from when he was just five, the day she walked out of their home, leaving behind unanswered questions about her departure and what became of her. Meanwhile, seven-year-old Katherine Fletcher learns she is adopted, which fills her with an unwarranted sense of shame. This feeling drives her to seek out her birth mother, a quest that has only grown stronger with time.