Resident Alien begins as a small-town mystery, but with a very large twist: the new town doctor, Harry Vanderspeigle, turns out to be an alien in a human suit. Even bigger than that twist in Resident Alien is when Asta Twelvetrees, a nurse who turns out to be Harry's first genuine friend on Earth, finds out about his identity. How then does Asta come to find out the truth? Not like a sweet repentance, but in the middle of a complete survival nightmare.
The truth is revealed in Resident Alien Season 1, Episode 8, “End of the World As We Know It,” when a rescue mission in the mountains goes horribly awry. Asta, Harry, and their daredevil pal D'arcy tumble into an ice crevasse, and Harry gets seriously hurt. His mask comes off as his human body is giving up. Not only does Asta receive an explanation, but she also gets a sight of the luminous blue blood and Harry’s true identity. Then, it is a turning point for both the characters: Asta switches her suspicion to clarity, and Harry needs to decide whether he wants to continue lying or trust the one human who rescued him.
The breadcrumbs before the big reveal

Way before the ice split disaster in Season 1, Episode 8 of Resident Alien, Asta always had a feeling that something was a bit amiss about Harry. He was too rigid, lacked social skills, and on many occasions treated people as his experiments rather than friends. She initially dismissed it as a mere quirky thing that doctors do, giving him the benefit of the doubt. The setup to the reveal develops early in Resident Alien Season 1 and boils over in the Resident Alien episode titled "The Green Glow," when odd signals in the mountains drive Asta and D'arcy to visit the backcountry with Harry.
Harry goes desperate trying to locate his “equipment,” and Asta can see that his panic is inconsistent with the story he is telling. The episode thrusts the two characters into an inescapable close proximity where the deception cannot continue. It is also full of playful tones, such as Harry breaking the pronunciation of his unpronounceable real name and making bizarre excuses to cover up the truth.
However, Asta’s instincts and gut feeling know that something is not right. The emotional ice between them finally melts by the time they are trapped by the literal ice cracking under their feet. Asta realizes it is time to know the truth, even if that truth is stranger than anything she could have dreamt of.
The moment when Asta learns the truth in Resident Alien

Trapped in the crevasse, Harry is wounded and bleeding, except his blood is not red. It is blue. His human mask is beginning to fall apart because of the injury and blood loss, revealing glimpses of his true alien body. Asta freaks out and wants to know what is going on.
Of course, Resident Alien's Harry, being Harry, attempts to lie first, explaining that it is some ridiculous allergy to snow bees or ice hornets. But the truth is too evident. In a dead end, he must confess: he is an alien. He says that he appears human most of the time, but when he becomes injured or under pressure, the disguise fails to hold.
The scene is hysterical, weird, and simultaneously intense. Asta is shocked but does what she has always done: she helps. On the orders of Harry, she burns his wound to prevent the bleeding. It hurts, yet it has to be done, and it somehow sparks an odd yet real connection between them. However, there is no going back to pretending after this incident. Asta is aware of the secret, and their friendship, for better or for worse, will have to face some repercussions.
What follows after
Getting out of the crevasse was just the first step. Asta races Harry to her father, Dan, seeking assistance, and in the process, matters get even worse: Harry indeed has to part with his leg, and Dan, subsequently, gets to witness what Asta had witnessed. At the episode's end, it is essentially Asta, Dan, and child-truth-teller Max who are aware of the true identity of the town’s local doc. That alters everything. Asta further becomes Harry's protector and moral guide, attempting to keep him alive and keep humanity safe from him as well. She establishes boundaries, imposes the regulations, and unconditionally clarifies that saving Harry does not have to be at the expense of jeopardizing others.
Their relationship grows throughout the second half of Resident Alien Season 1 and beyond, with certain scenes in which Asta more blatantly declares that Harry will have to kill her before harming anyone else. Their friendship does not end after the big revelation about Harry's identity; rather, that incident redefined their connection. Whether it is impossible decisions or emergency amputations, Asta continues popping up in Harry's life, and the latter continues to learn what makes humans worth the trouble.
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