On Teen Wolf Season 6 Episode 19, Argent goes to Brazil looking for Derek. He wants Derek to join the fight and return to Beacon Hills. It turns out Derek is in Brazil to stow away poison because he knows Gerard wants it.
In Beacon Hills, Deucalion attempts to teach Malia and Scott how to fight blind. Meanwhile, Nolan approaches Liam, offering to help.
Nolan tells Liam about how many people have joined Monroe's army -- these people include doctors and nurses. Nolan then takes Liam to the ICU where a bunch of people are hooked up to wolfsbane IVs.
As Argent and Derek approach (yet another) Hale vault, they are approached by the federal government, except one of those "agents" is Kate Argent. She steals the poison, saying she is going to put it in a bullet and kill Scott.
Derek goes after Kate and tells Argent to go back to Beacon Hills to warn Scott.
Nolan leaves Liam in the ICU, and on his way out of the hospital, he runs into Gabe. Gabe tells Nolan that Monroe knew he would rat them out. It was all part of the plan.
Sure enough, when Mason and Corey arrive at the hospital to help Liam, they quickly realize that it's a trap. Soon after their arrival, hunters arrive and lock the hospital down.
Lydia confides in Peter that her latest vision featured everyone, including Derek and Ethan, turned to stone. They manage to catch up with Scott, Malia, and Deucalion at the ship yard where they give them a brief head's up that Monroe and the hunters are coming.
Then, the gunfire starts, and Deucalion goes down.