The War Within

 is a cinematic quest released in Update 19. It explores the story of the Twin Queens and Teshin.

Walkthrough
The player must have a Mastery Rank of at least 5, complete The Second Dream quest and have completed the Sedna Junction at Pluto in order to start this quest.

If the player has accomplished all the necessary prerequisites, an e-mail from the Lotus will arrive in the player's inbox with the following message:

"Something has happened on Lua and my spies have become unresponsive. I need you to investigate immediately."

- The Lotus

The quest can then be activated in the Codex under the Quests section. A short cinematic will then play, showing the Twin Queens in their lair. Back on the Orbiter, the Lotus worryingly asks about the Operator's state due to high Somatic output. After the Operator reassures the Lotus of their condition, they are asked to deploy a Warframe to Lua to investigate the missing spies.

Investigate the Reservoir on Lua: Zeipel, Lua
Landing on Lua, the Lotus narrates how they are now in the place were Margulis tried to save the Tenno, stating that all Tenno were born there. As the Operator tries to clarify whether they were truly born there, the Lotus relates that they were the only things saved from the Zariman as the Orokin tried to rectify their mistake. Detecting an unusual signature within the vicinity, the Lotus asks the Tenno to investigate.

Deeper in the facility, the Tenno will encounter a shadowy being that can seemingly teleport, with the Operator reporting that they think the intruder is Teshin. Confused as to Teshin's presence, the Lotus asks the Tenno to track him down, seeing as how he is heading towards the reservoir.

Through a transmission, Teshin asks the Tenno, whom he refers to as a "child", to leave as the matter at hand doesn't concern them. Annoyed at Teshin's behavior, the Operator asks what he is doing. When the Tenno finally catch up to Teshin, they see him in the reservoir performing an unknown task, and hearing a female voice asking Teshin to bring something to them. Asking as to the identity of the female voice, Teshin reveals it to be "the queens", which the Operator immediately recognizes as the Grineer's Twin Queens. Teshin draws his sword to the Warframe's neck when the Tenno get too close, warning them that they are not as safe behind the Warframes as they think, and that Teshin will fight them if they attempt to follow him.

Casting a decoy of himself, Teshin escapes, leaving the Tenno behind to deal with the Specters left in his wake. As the Lotus has difficulty tracking Teshin through his signal masking, the Operator asks the Lotus to focus on tracking him as they deal with the Specters.

''WARNING: The walkthrough ahead contains significant spoilers to Warframe's lore. It is recommended to play through the quest first.''

The War Within is automatically made available upon completing the Sedna Junction. The Quest can be activated in the Quests section of the Codex.

Track Teshin: Carpo, Jupiter
Tenno have to locate and capture another of Teshins specters.

Pursue Teshin into the Asteroid Field: Naga, Sedna
First part of the mission is an archwing infiltration, where Tenno have to hide from scanners over sides of grineer shuttle.

Second part is defense. Tenno have to hold off Kuva grineer while security is being disabled.

Proceeding to the next part of quest will prevent player from switching to other missions.

The Ravenous Golden Maw
Three choices:
 * [White] I held out hope
 * ...that we would be rescued. So I avoided the bloodshed.
 * [Neutral] They had lost their minds
 * [Black] They were nothing but animals

The next three choices:
 * [White] I hated it
 * [Neutral] I controlled it
 * [Black] I embraced it

Stun the guardians with void blast and disarm them with void dash, they will be vulnerable while disarmed. Destroy braids with void beam. Defeat Teshin, and do as he says.

The next three choices:
 * [White] Let her rot
 * [Neutral] I will do it
 * [Black] Kill her

Return to The Mountain Pass: Earth
Recharge aytan with void beam, dash up to slabs.

The next three choices:
 * [White] Destroy
 * You mad at me, kiddo? Did you forget?
 * You owe me.
 * [Neutral] Control
 * [Black] Consume

Aftermath
Once quest is finished Teshin will send a letter, that asks to forgive him. There are 4 attachments to it: Broken Scepter, Orvius Blueprint, Riven Mod, and Grineer Queens Glyph.

Trivia

 * The Lotus already hints to The War Within during her final conversation with the Tenno at the end of The Second Dream.
 * As in The Second Dream, alterations to game mechanics are planned.