Sam is itching to get back to work, so he finds a potential case in the form of a taxidermist who was crushed to death. Dean is all, "You can't go back to work! You're still incredibly weak even though you mysteriously feel 100% better!" Sam's like, "All right, explain what you just said." And Dean's all, "Let's go work that case now!" So off they go, with a completely off-screen Kevin doing much of their research for them.
At first, signs point to a couple of animal rights activists who are down on all the hunters that frequented the taxidermist. The brothers soon learn that the activists were also attacked that night, when someone sprayed venom in their eyes. The next attack has the brothers checking out the local animal shelter, where a hapless victim was murdered after discovering a man making Tender Vittles out of a couple of cats. The Winchesters are stumped. What kind of supernatural creature has claws, venom, and the crushing strength of a boa constrictor? While at the shelter, they notice that the taxidermist's German Shepherd dog has been brought in. Realizing that ol' Colonel may be the only witness to the crimes, they take the pooch back to their motel room.
But how to communicate with Colonel? Kevin provides them with an old Inuit spell that will allow one of them to communicate with the dog. Dean volunteers, but somehow ends up being able to talk to all animals instead of just the one. All the animals talk in terrible, cartoonish human voices. But, wait! It gets worse! Dean also begins taking on some canine personality traits, like wanting to attack the mailman, play fetch, and stick his head out of car windows. Sadly, because this is Supernatural, we cannot escape the episode without not one, but two bestiality references. First, Dean eye-humps a French poodle, and then a Yorkie bribes Sam into rubbing his belly in a fairly lascivious manner. The rubbing pays off, though, and the Yorkie says he saw the fellow who ate the cats. Luckily, the Yorkie is also literate, because he was able to read the name of a fancy restaurant off the guy's bag o' cats. Dean frees all the dogs from the shelter in a sudden fit of empathy.
The Winchesters track down the culprit and learn that he's a chef who's been cooking and eating weird animal bits to help heal himself of cancer. The bits also give him magical properties associated with their corresponding animals, but thus far none have put his disease into remission. He's inspired anew after he attacks Sam and witnesses him recover almost immediately. Not realizing that this is Sam's inner angel at work, he thinks eating Sam's heart will imbue him with similar healing abilities. Naturally, because he's a bad guy, the chef takes way too long in explaining all his evil plans, and those dogs that Dean freed earlier show up to save the day. It's like the ending of a Disney movie, but with more of a "dogs eat a guy to death" angle.
In the end, Colonel finds a new home with the activists, who promise him all the vegan food he can eat. Sam wonders why weird things keep happening, like why did that evil chef think he had magic healing properties? Dean lies unconvincingly yet again, but Sam doesn't press the issue, because this plot is going to keep dragging like a dog with an itchy ass across the carpet. Stay tuned for the full recap, and bring a pooper scooper.
THEN! Sam's innards were barbecued by those hellish trials, so Dean called out to any available angel to heal him. The call was answered by an angel named Ezekiel, who was wearing Tahmoh Penikett's body at the time. After creatively redefining "consent," Zeke possessed Sam to heal him from within. This resulted in a winningly terrible performance from Jared Padalecki as a strangely robotic angel. Zeke was supposed to just hole up in Sam for a little while, but Show kept finding ways to keep him around. He had to use his powers to dispatch a gaggle of demons, bring Castiel back to life, and then save Charlie when she sacrificed herself to protect Dean. All this Zeke ex Machina stuff meant that he had to stay longer and longer in order to heal himself, as well as Sam.
They could have left off right there and started with the episode, but they decided to remind us of (mostly) better and/or funnier episodes from the past.
The Dean of several seasons ago reminded Sam that they would hunt people and save things like their dad. Sorry, no, that's hunt things and save people. Sometimes it's easy to get them mixed up. Anyway, Dean once met a fairy who beat him silly, and narrowly avoided getting squashed by a cartoon anvil. Oh, hey, and remember that time he got the fear rash that made him scared of harmless kittens and puppies? Then there was that time he met the suicidal teddy bear, and that time Sam got punched in the nuts during a Japanese game show. Oh my God, and the time that Sam adorably lost his shoe? Priceless. Now, forget all that stuff, because it will just make you cry about how much better the show can be. Instead, concentrate on the show's weird history with horny dogs and the people who love them, because that's more the level of this particular episode.