The Sacrifice continues the story that began with The Second Dream and War Within revolving around the creation of the Tenno and the subsequent destruction of the Orokin. At E3 2018, a short trailer for The Sacrifice was unveiled showing us the Umbra Warframe in a fair amount of pain as well as Ballas, an Orokin Executor.
Ballas is credited with the creation and perfection of the Warframes, continuing the work started by Margulis to help the children of Zariman 10-0 control their unstable void powers.
The trailer, which offers such a tantalising glimpse at Umbra and the story that will unfold in The Sacrifice, shows Umbra howling desperately with Lua in the background. Lua also known as the Orokin Moon, was the seat of Orokin power during their reign, which was placed into the Void by the Lotus to hide the secret of the Tenno.
We also see the hunched figure of Teshin behind Ballas as the latter states that we cannot bring him back. It would seem that Teshin is going to be a key figure in The Sacrifice, and the events that surround Umbra.
A popular theory is that Ballas has removed the control of the Operator, the Tenno, leaving Umbra at his will. But with the release of The Sacrifice scheduled for later this week, all secrets will be unveiled soon enough.