'Black Rain' may be the best use of ironically cheerful music yet on Helix.
Day 11 begins with a starving woman, Doctor Kato, scrounging for food. She is distracted by a rat in a microwave. When she moves toward the microwave she is taken by two vectors while Peter watches from behind the rat which explodes inside the microwave.
Elsewhere, Hatake gets a message on Sutton's phone telling her to check in with the bosses. Balleseros' failure to check in is what brought Sutton to the base to begin with, so Hatake know that something big is coming. He gets a case full of bombs out of a secret compartment and plants them all over the base.
In the medical unit Julia and Sarah are recovering after Julia's spinal fluid was used to treat Sarah's tumor. Alan enters and Julia tells him that her cells and Sarah's work with them are the key to curing the disease. Doctor Duchamp arrives to tell Alan that the vectors are kidnapping people and shows him the microwave. In front of the nuked rat's remains Alan says that the virus and vectors have evolved.
Hatake tells Alan that they have 6 hours before Ilaria comes for the virus. When Miksa enters Hatake tells the other two about his bombs and a secret bunker. Alan meets up with Duchamp in the storeroom where most of the remaining healthy people have been gathered. Duchamp is getting paranoid so Alan tells him that there may be help on the way while vectors watch from inside the wall.
Miksa is still angry about all of the secrets Hatake has kept from him, including the bunker and it's escape tunnel. Hatake stands by his secrecy but tells Miksa that he needs him as the world closes in on them. Later they inventory weapons and grumpily reminisce about Hatake teaching Miksa to use a gun, and Hatake insists that Miksa is still his son.
Julia wheels a cart carrying science equipment into the medical unit and gets back to studying her cells, along with the Narvik virus. She gets close to a cure and tells Alan she got there using Narvik, which he thought was destroyed. He gets angry and compares her to Papa Hatake. Sarah interrupts their reconciliation by throwing herself against the glass. They all gather around her bed and discuss the cure. Sarah has the idea to combine it with cryo fluid to give it time to take effect by slowing the virus down.
Meanwhile the vectors are working working like bees on a plan. They force Kato onto a bed and cut her arm, making her bleed into a bucket.
Hatake takes Miksa to the bunker, which is Julia's childhood home. He tells Miksa that Julia is his daughter and he does not take it well.
Above the storeroom where Duchamp and the extras are gathered Peter pours Kato's blood into the sprinkler system and turns them on, infecting everyone but the main characters and some of Miksa's security team, all while Buddy Holly's "Raining in My Heart" plays.
Alan says that they fell right into the vectors' trap. He and Hatake butt heads once again when Hatake suggests going straight to the bunker and waiting to blow up the vectors and Ilaria at the same time, but Alan insists on staying until the last minute and administering the cure. Julia tells them to stop their fighting as it is tearing her apart and teaches them the value of teamwork. She mentions that Hatake is her father, which no one told Sarah and her "what?" is perfectly edited and it isn't brought up again.
The team gather around and tries to think of a way to freeze the vectors so they be cured. Sarah says it's a shame they can't use the big tanks of cryo fluid and Miksa says he may be able to make that work. He shows them the device he made for spraying fluid and Hatake swells with pride.
Hatake and Julia put on haz-mats and begin to find and cure vectors, starting with Peter. Hatake does the cryo spraying and Julia handles the pharmaceuticals. After curing at least five vectors in addition to Peter, Hatake and Julia leave and behind them some still-infected vectors get into the vents.
While caring for the recovering vectors Sarah gets a headache and worries it may be from her tumor. Alan assures her that it is not.
When the alarm goes off alerting everyone that Ilaria has arrived Hatake, Miksa, and Doctor I-didn't-like-guns-but-then-I-used-one-and-now-I'm-OK-with-them Farragut take up machine guns to hold them off. Just as they prepare to fire the fleet of snowmobiles suddenly stop. Upon further inspection they find that the snowmobiles were riderless drones sent to distract them from the trio that falls from the sky. One of the drones explodes and Hatake is injured.
In the bunker Hatake say that there is not a strike team, but just one person that they have to worry about. He says he is the most dangerous immortal, an assassin called the Scythe.
The Scythe and his companions, all wearing masked helmets, get to the elevator bringing down the last of the newly cured. Duchamp is at the front and he asks if the Scythe is with the rescue team. He nods and they get in the elevator, killing everyone before it reaches the ground floor.
Sarah has another headache, but this time Julia recognizes the symptoms from her transformation into a silver eyed immortal. Miksa goes to pull the trigger for the bomb, and Alan complies, but when he does nothing happens.
The Scythe finds that the Narvik is missing and assumes Hatake has it. He tells his henchwomen to find Hatake and exterminate everyone else as he removes his helmet, revealing his very young face.

image courtesy of Syfy/NBC