This week starts out with Mother hitching a ride with a truck driver. She whispers in his ear and then he goes and murders his family. Bobby and the Winchesters see a string of murders and go and investigate. Booby sure cleans up playing an FBI agent. They run into Rufus and he's there to investigate the same thing. So Rufus and Bobby go to see the body of the latest killer and find some goo in the ear. They figure out it's some kind of parasite and follow it to a warehouse where they run into Samuel and Gwen. Of course Dean is true to his word and goes to shoot Samuel but gets stopped by Sam and says they need to work together. Dean is alone with Gwen and shoots her and runs. They figure out it's in him but when they catch up to him, he's himself again. Then it goes into Samuel and he sets up traps for them and Sam gets separated. He runs into Samuel and shoots him in the head thinking he has the parasite. Well they are unsure until they can cut Samuel open so they tie up Sam's hands. Rufus and Bobby go to cut up Samuel's head and send Dean and Sam outside and as they start cutting, Samuel sits up. They end up electrocuting him and the worms slips out. Sam and Dean come back in and since no one knows where the parasite went they all must be zapped to be tested. Dean goes first, then Sam, then Rufus and when they get to Bobby he's reluctant and he stabs Rufus.
They tie Bobby up and try to figure out how to get the parasite out of him without killing him. The parasite tells them that Mother of All cooked him up and she has new monsters they've never seen. Her plan it to take over earth with her monsters and eliminate humans. They zap Bobby and the parasite dies and we are meant to believe Bobby died too. The next scene is Dean and Sam looking down at a grave but then Bobby comes and they are actually looking at a grave for Rufus.
So three people died in this episode, Gwen, Samuel and Rufus.