Last week, we showed you both a new poster and a video that touts the return of Jaimie Alexander's Lady Sif on this week's episode of Marvel's Agents of S.H.I.E.L.D. titled "Who You Really Are". Before the new episode debuts tonight on ABC, the network has released yet another poster featuring Lady Sif brandishing a sword and the tagline "Old Allies Return." Unfortunately for the Marvel's Agents of S.H.I.E.L.D., Sif may not be much help to them.

Tonight's episode centers on Coulson and his team as they come to the aid of a confused Lady Sif, who has lost her memory after fighting with a mysterious warrior, whose true mission will send shockwaves through S.H.I.E.L.D. Meanwhile, Bobbi and Mac continue to hide their true mission from everyone close to them. When Lady Sif last appeared on the show, she shed some light on the mysterious blue alien corpse that saved Coulson's life, which was later confirmed as a Kree corpse. It seems we'll be learning even more about the Kree in this episode.

Marvel has released two mysterious alien headshots that certainly seem to be of Kree origin, but they didn't release any further details, or reveal how this blue-skinned alien fits into the story. Even though Sif is said to have lost her memory in tonight's episode, it's possible she may be able to shed some light on the Kree and how they fit in with the Inhuman transformations of Skye (Chloe Bennet) and Raina (Ruth Negga). These images are said to "foreshadow some surprise revelations in this week's episode," but we'll have to wait until tonight to find out for sure. While we wait for tonight's episode to air, check out the Lady Sif poster and mysterious alien headshot photos, and chime in with your own theories below.