In the wake of her recent battle with Red Tornado, Kara's powers are drained. She is told by the Kryptonianartificial intelligence at the Fortress of Solitude that her powers will return in a few days, but she is concerned about her powers never returning. Alex tells Kara that she doesn't trust Hank anymore and urges Kara to enjoy a day without her powers. At work, Kara is sick. Winn offers to do some research on a shortcut to reenergizing her powers, but when Cat arrives at work, she sends Kara home to avoid catching her cold. Kara and James bump into one another, and he tells her that he and Lucy are moving in together. Just as Jimmy tells Kara agree that "the world can survive one day without Supergirl," an earthquake knocks them both to the ground. In the ensuing chaos, Kara nearly gets hit by a car before Jimmy pushes her out of the way, inadvertently breaking her arm. On the walk back to work, Kara sees all of the destruction of the city that she could've stopped if she had her powers. At CatCo, the essential personnel still working through the earthquake watch as Maxwell Lord criticizes Supergirl for not saving the city from the aftereffects of the earthquake. When Kara and Jimmy visit Maxwell, he is unfazed and claims that Supergirl has drained her powers and may never get them back. Maxwell attempts to save a woman's father in front of Kara and James, but in the absence of an X-ray machine to find a venous thrombosis, he fails. Without her power of X-ray vision, Kara is unable to save the man as well, making her feel helpless. She is heartened when, dressed as Supergirl with her broken arm still shaking, she is able to talk down a robber. James captures a photo of their confrontation. James shows Kara the picture he took of her and the two share a moment. Winn, who has just found a way to kickstart Kara's powers, walks in on them hugging. He awkwardly mentions that an adrenaline rush will help reignite Kara's powers before leaving upset. An earthquake-triggered gas leak results in a fire on the upper floors of the CatCo building. While climbing up the elevator shaft to help their trapped neighbors, Jimmy loses his grip and ends up clinging to the thinning elevator cables. Just as he falls down the shaft, Kara suddenly appears in her Supergirl uniform, flying down to rescue him before traveling across the city to save the day. Back at the Department of Extranormal Operations, a psychic alien known as Jemm plans to escape. The earthquake also causes damage at the DEO, causing a power outage and an opportunity for Jemm to escape his cell. Hank and Alex seek out the Kryptonian artificial intelligence for advice and gather a teamto go after Jemm with neural inhibitors. Hank asks Alex to stay behind with the rest of the team. Alex watches on the monitors as Hank's attempt to take down Jemm fails. Hank returns and warns Alex that Jemm has seen the thoughts of the other DEO officers, giving him the upper hand. Alex, who still believes Hank is hiding something, and another agent follow Hank when he goes to fight Jemm again. Jemm uses his powers on Alex's partner and kills him just as Alex is tackled into a room by Hank. Alex makes Hank handcuff himself to a wall, revealing she knows about his connection to her father's death. Jemm comes looking for Alex, who successfully attacks him. However, Jemm gains the upper hand and prepares to finish her off when he is suddenly attacked by Hank. After a short and brutal fight, Hank snaps Jemm's neck. Hank then turns on the lights and tells Alex that he’s not the enemy. Confused by his escape and motives, Alex demands answers. He confesses that he is not Hank Henshaw, but rather the alien that Alex's father died saving. He reveals himself as a shapeshifter who copied Henshaw's appearance in order to reform the DEO. He identifies himself as J'onn J'onzz, the last surviving member of the Martian race. He also tells Alex that he promised her father that he would look after her, hence her recruitment into the organization. Later on, Kara invites Winn home, but he declines, saying he’s never disappointed in Supergirl but disappointed in her. Supergirl speaks with Cat, and, on her way home, is suddenly attacked by three Kryptonians, led by her Aunt Astra.
Reception
Ratings
The episode attracted 856,000 viewers for its British premiere, making it the 3rd most watched programme on Sky One for the week.
Critical response
Jeff Jensen of Entertainment Weekly noted: "'Human for a Day' tackles one of the biggest tropes of the superhero genre: a powerless superhero. The point of stories like this is to show that being a superhero doesn't just mean having powers, and the show's exploration of this theme is quite effective. A powerless Kara also allows for characters like James, Cat, and Alex to shine." Cliff Wheatley of IGN gave the episode an 8.6, saying "Human for a Day" achieves its goal in showing us why Kara is a hero with or without superpowers, while also delivering big on the hype of introducing a new DC superhero to the fold. Jemm is a definite weak link and Winn is still struggling to stay relevant, but Supergirl's latest is a definite winner. Stacy Glanzman of TV Fanatic gave the episode a 4.3 out of 5 stars.
