What's Going on With Guillermo in "What We Do in the Shadows"?

Watch out! This post contains spoilers.

At the end of "What We Do in the Shadows" season four, Guillermo (Harvey Guillén) makes the drastic decision to ask Derek (Chris Sandiford) to turn him into a vampire. Fed up after years of his master, Nandor (Kayvan Novak), ignoring his pleas, he decides to get it done himself.

But at the beginning of the show's fifth season — which premiered in July — we find out Guillermo's turning didn't work. Or it did work, but only a little bit. At the start of the season, it's been 16 days and the typical vampire powers haven't fully come in for him, which is highly irregular. Guillermo can still eat food (though he does crave very rare meat) and go out in the sun. He can't, however, turn into a vampire bat and fly away.

Over the course of the season, we ultimately find out why Guillermo's transformation didn't work. And when Guillermo and the vampires finally solve the problem, he makes a complicated decision. Ahead, we're breaking down Guillermo's vampire journey, why he's not a vampire at the end of the season, and what it might mean for the show's sixth season.

Guillermo learns early in season five that having a vampire who's not your master "turn" you is a massive slight, which he didn't know. Laszlo (Matt Berry) calls it the "greatest humiliation" a familiar can inflict on his master, and Nandor says that if Guillermo did it, he would kill him and then himself. Guillermo's in a tough spot, as he also can't have Nandor bite him and pretend that Nandor turned him. Why? Apparently, getting bitten twice makes a vampire explode.

In the third episode, which aired on July 20, Laszlo helps Guillermo investigate the weirdness of his transformation. He has small, fleshy bat wings on his back, but he's not any faster and unaffected by garlic. He does have some telekinetic powers and lifts a glass with his mind. We also learn of a stereotype that if you spill rice, a vampire must count it all. Laszlo and Nandor do just that, but Guillermo doesn't share their compulsion. Laszlo also discovers Guillermo's sweat is the key to his ability to go safely in the sun, though they can't agree if that makes him a day-walking vampire like Blade or not. Laszlo decides that Guillermo's transformation has been "stymied." Later in the season, he uses Guillermo's blood to make animal-Guillermo hybrids (which are seriously creepy), but the secret to what's keeping Guillermo from fully transforming remains a mystery.

In episode six, "Urgent Care," which premiered Aug. 10, a vampire doctor informs Nadja (Natasia Demetriou) that Guillermo's blood signals that he's turned, but he's still in very early stages. And by the end of episode eight, which aired Aug. 25, basically all the vampires know about Guillermo's secret — except for Nandor.

We had lots of theories about what would happen heading into the final two episodes of the season. Viewers learned in previous seasons that Guillermo is a descendant of the legendary vampire hunter Van Helsing, which explains why he's such a wonderful vampire killer (or defender when the coven needs him to be). Many wondered if there was something in Guillermo's DNA that kept him from fully transforming. It seemed possible this made him an undead vampire killer.

Other fans speculated Guillermo is a Dhampir, a mythical creature that is the child of a vampire and a human. Getting bitten only brought out some of the vampire characteristics that were in him all along. There was also the theory that Guillermo's transformation wasn't working correctly because he didn't have his master do it for him.

When Nandor finally finds out that Guillermo is a vampire, after some initial anger he decides to help him. He agrees that Guillermo's transformation was stymied by his Van Helsing DNA. He gives Guillermo the thing Laszlo never thought of: a glass of human blood. This finishes his transformation, and Guillermo is a full vampire, finally.

Pretty much immediately, Guillermo starts to realize that all the murder that comes with vampirism is not for him. Nandor realizes this, and he decides to help his former familiar out. He uses a pretend ceremony to get their whole vampire circle together, including Derek. And when Guillermo admits he wants to be human, Nandor kills Derek. Since Derek sired Guillermo, this reverts Guillermo back into a human. Killing a sire will get rid of all the vampires they created.

Guillermo feels bad about Derek's death, and he and Lazslo bring his body to a necromancer to turn him into a zombie. As Guillermo heads into season six — having achieved his dream and then immediately given it up — it'll be interesting to see where his journey with Nandor takes him.

Season five of "What We Do in the Shadows" is streaming now on Hulu.