4x13 - Blue Murder

When the mummified remains of an infant are found inside a tree, Weeks and Bender investigate the former residents of the house and learn that the baby was never registered, and the suspects include the mother, who is completely out of touch with reality, and her husband, an ex-convict who is not the baby's father. Ed's former fiancée Marissa calls him in for help when her parents disappear, but it's only a matter of time before Stahl and Oosterhuis discover that Marissa's parents are involved in an elaborate con to bilk people out of their hard-earned money.