Til Death Do Us Part is the eighth episode of the third season of Siren. It aired on May 14, 2020. 
Ryn, Ben and Maddie must protect Bristol Cove from Tia's army. Meanwhile, Ben's injections are producing unexpected results, which alarms both him and the others. Xander juggles best man duties at Calvin's wedding while also helping Helen.
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Jerry serves as the minister who pronounces them husband and wife.
Chris makes his first appearance since "Sacrifice".
This episode was directed by Bola Ogun who directed, produced, and starred in a short film titled The Water Phoenix, in it she played a mermaid protagonist held captive in an aquarium.
Employees at a municipal office in Ternipol, Ukraine suffer the dissonance of the Siren Song. It is revealed that the Russian government's reason for lobotomizing Tia was to weaponize her song to use against other countries.
In Vladivostok, Tia reunites with a man named Boris. In a hotel room, they share a moment of intimacy, and then Tia asphyxiates him. She searches Boris' laptop and uploads the audio file of her Siren song to a flash drive.
Alexei is the name of the scientist who performed the lobotomy on Tia, he was the one who weaponized her song. He was suspected to have helped Tia escape.
Ben gives himself another injection of the mermaid stem cells making a total of 8 doses, this allowed him to remain underwater for 15 minutes. After exiting the water, he starts breathing shallowly, then webbing forms syntactically between his fingers and gill slits appear on his ribs. Although temporary, this was much to Maddie and Ryn's surprise.
Donna's corpse is buried into the ocean in order for her spirit to be at peace.
As a result, Chris has broken free from her Siren Song and Helen is no longer being haunted.
Xander is right. Hope will live under Tia's rule if we don't stop her. We must ask the military for help.
— Ryn to Ben and Xander
They get suspicious when you do not drink here.
— Tia to Hunter while drinking shots.
Never underestimate a higher life form.
— Helen to Xander
When it is time... I will be human with you.
— Ryn and Ben discussing their options
My mother and I had a special place in the water. The last time I saw her, we went there. We hunted. Mother. Daughter. Together. Now we will bring her back home.
— Cami's eulogy to her mother Donna
Humans think you're apart from someone just because they're not physically with you. But we know, don't we?
— Helen to Ryn, reminiscing about Sarge's spirit
Siren Season 3, Episode 8 Trailer The Song Is Weaponized
Siren Season 3, Episode 8 Sneak Peek Will The Military Help With Tia? Freeform
Siren Season 3, Episode 8 Sneak Peek Ben Gets Ready To Fight Underwater Freeform
Siren Season 3, Episode 8 Sneak Peek Xander Notices Something Weird In Chris' Room Freeform
Siren Season 3, Episode 8 Ben Starts To Transform Freeform
Siren Season 3, Episode 8 Ryn & Cami Return Donna's Body To The Sea Freeform
Siren Season 3, Episode 8 Janine & Calvin's Wedding Freeform
Siren From Storyboard to Scene Season 3, Episode 8 "'Til Death Do Us Part" Freeform