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For the group of superheroes, see The Trinity.
"Reign, Purity, Pestilence, they were all created by Kryptonian witches to do one thing: kill the world. And now that they're together, they're doing that."
Kara Danvers

"Trinity" is the seventeenth episode of the third season of Supergirl, and the fifty-ninth episode overall. It aired on May 7, 2018.




Guest starring[]



"Trinity" begins with Lena being addressed by the DEO. Kara asks Lena how she had the option to keep Sam contained. Lena uncovers she utilized kryptonite in Sam's holding cell.

The Worldkillers have gone to Reign's Fortress of Sanctuary. The trio starts doing a ritual when Sam out of nowhere awakens in the pocket dimension we saw a week ago. She's before long joined by the human alter-egos of the different Worldkillers.

Lena calls James and apologizes for keeping secrets from him. She tells him that Sam is Reign. She concedes that she failed Sam. Kara interrupts their call, making Lena guarantee she has no more kryptonite.

Kara unexpectedly enters the pocket dimension where she sees Sam. She discloses to the remainder of the DEO that while there isn't an end of the world in the Book of Rao, the ancient book clarifies how the Worldkillers play out a "Blessed Darkness."

They conclude that some way or another Kara needs to enter the different pocket dimension to stop the Worldkillers. They trust Brainiac-5 with utilizing his 31st innovation to attempt to connect her mind into the other domain. It's concluded that both Lena and Alex will travel to the pocket dimension with Kara.

Sam and Julia — the human alter-ego of Purity — are working through the valley when the last continues seeing individuals she's murdered. Julia begins separating until Sam reminds her to take a full breath and consider another thing to occupy her psyche. Sam at that point recalls about her little girl Ruby and starts to forget who she is.

Kara flies to CatCo to converse with James about Lena having kryptonite. Kara declines to totally trust Lena and requests that James poke around and see if Lena has any more kryptonite.

On the Legion's ship, Alex approaches Lena about the tests she ran on Sam. Lena guarantees that Ruby is protected. Kara shows up on the ship and Brainiac-5 discloses to her that he has figured out how to communicate with their consciousnesses, however the more individuals that enter the pocket dimension, the weaker they get.

Kara pulls Mon-El aside and discloses to him that on the off chance that anything begins going south, to pull Alex and Lena out of the dimension. Brainiac-5 beginnings the way toward broadcasting the three into the pocket dimension.

Kara, Lena, and Alex before long stumble upon the body of Grace, the human form of Pestilence. She's dead.

Brainiac-5 is counting down the time before they have a full eclipse, which would mean the Worldkiller's ritual worked, which would thrust the world into darkness.

James gets ready as Guardian and with the assistance of Winn, gains admittance to Lena's lab.

In the pocket dimension, the group is contending about Lena's use of kryptonite when a Kryptonian Demon starts flying around them. Alex can utilize a stick to scare the evil spirit off and the trio proceeds with their quest for Sam and Julia.

They before long discover Sam and Julia, who are in a type of mental states, mumbling rubbish.

James is checking out Lena's lab when he has a change in heart. Not wanting to break Lena's trust, James reveals to Winn that nothing is in the lab, in spite of the fact that there is a safe in the room that could be hiding something.

Alex and Lena begin conversing with Sam, who comes to and realize who she is. Sooner rather than later, Reign discovers that they're conversing with Sam and Sam's eyes turn red. Reign has switches places with Sam in the pocket dimension.

Sam/Reign starts choking Lena when we discover Sam's consciousness in now in Reign's body on Earth. She makes the DEO aware of the area of the Worldkiller's Fortress. Imra and Brainiac-5 take the three out of the pocket dimension. They start to design an ambush on the Fortress.

Winn bestows Alex with another uniform and some tech, including a powerful magnet and a new gun.

Kara, Mon-El, Imra, J'onn, and Alex start battling the Worldkillers as Lena remains on the Legion ship to help Brainiac-5 and Winn pilot it.

Team Supergirl is getting bested but are able to help Julia regain control. Julia is able to use Purity's powers to fight against Reign and Pestilence. Pestilence cuts Purity, yet Purity utilizes her sonic forces on Pestilence, slaughtering her. Purity also dies.

Their spirits are evidently consumed by Reign before the Fortress of Sanctuary starts disintegrating to the ground. Team Supergirl escapes.

Back at the DEO, Mon-El and Imra are celebrating about stopping the Worldkillers. They decide it's an ideal opportunity to return home. Imra leaves the room and Mon-El seems to think again.

Kara shows up and tells J'onn and Alex that the Fortress of Sanctuary has deteriorated, however Reign/Sam is mysteriously gone. Winn discloses to Kara that he and James looked through Lena's lab and discovered no additional hints of kryptonite.

Hearing the phony news, Kara approaches Lena and discloses to her that their record is spotless.

Lena converses with James at CatCo. James concedes that he initially thought Lena was a carbon copy of Lex yet in the course of recent years, she's kept on proving him wrong. James uncovers to Lena that he's Guardian. He reveals to her that he broke into her lab on Supergirl's requests. He reveals to her he didn't go into her vault since he trusts her.

The two embrace and Lena reveals the kryptonite wasn't her brother's; she discovered how to make it.

The episode ends with Reign hovering over the city, receiving a message from Selena that "Ruby Arias must die." At the same time in Juru, Sam touches her daughter's name and screams.




  • The episode's title refers to the Worldkillers - Reign, Purity, and Pestilence.
  • This is the third episode of Supergirl where Kara appears only as Supergirl, the first two being "Resist" and "Of Two Minds".
  • One of the names Julia writes in the cave is "Peter David". Peter David was a writer of the Supergirl comics for many years.
  • Kara is unusual upset with Lena about the Kryptonite; given she wasn't this angry at J'onn.


  • Katie McGrath slips into her native Irish accent at several points throughout this episode.