Roadkill

At Greely's grave, Sam explains to Molly the weaknesses of a ghost. To "kill" a ghost is to burn the remains such as bones, hair, and anything that has the DNA of that ghost. After burning the corpse, Molly still looks for David but Sam hesitates to tell her. Suddenly, a strange figure grabs Molly and dives into the water. Sam and Dean quickly runs to Molly's rescue while thinking about the ghost and who is it. Dean and Sam looks at each other and the two split.
Sam rescues Molly as Marion fades temporarily. Marion is ghost who wants people who lost their loved ones to suffer like her. Meanwhile, Dean heads over to burn Marion's corpse, but the rain wet the flames and he runs out of oil. Dean burns his shirt to destroy Marion's ghost.

Sam and Dean drives Molly to David's house. Sam reveals to Molly that David remarried and Molly died 15 years ago. Sam explains that the two ghosts, Greely and Marion, uses Molly to lure victims and that Molly is stuck in time. The reason that Molly cannot cross over because she cannot remember. Sam tells her "It's time you say good-bye to him" because David said good-bye to Molly many times. With that quote burning in Molly's head, Molly hugs Sam and thanks Sam. Molly says good-bye to David as she crosses into the afterlife.