Dean is determined to get on with the "family business" to the best of his ability, before the Mark of Cain takes hold of him irrevocably, yet Sam is still desperately looking for a cure.
Dean suspects Sam is hiding something but decides to focus on a murder case in an army town, where the clues lead to a pair of soliders who returned from an overseas deployment "changed".
One has killed himself, after brutally murdering someone, but the other is Kit Verson (Richard de Klerk), who happens to be an old friend of Cole Trenton (Travis Aaron Wade).
At first Cole is a fly in the ointment for the Winchesters, determined that Kit needs "help" rather than "putting down", but eventually - after he becomes infected as well - Cole realises the enormity of the burden that the Winchesters bear.
The Things They Carried, scripted by Jenny Klein, is a superb tale, managing to be a metaphor for Dean's situation as well as a strong, yet fresh, 'monster-of-the-week" episode.
The story demonstrates the legwork and methodology of the monster hunters, and deals with the fact that sometimes there are alternatives to putting a bullet in the brainpan of the creature (or the meat-suit it is inhabiting) they are facing.
Everything about this episode (such as making Dean the one seeking a non-violent resolution to the situation) works perfectly.
This season, in particular, could have done with more episodes as solid as The Things They Carried.