The Ambush at the Distant Star Facility was a successful attempt by HYDRA to kidnap Leo Fitz and Jemma Simmons, whom they believed could help HYDRA achieve their oldest goal, retrieving their leader from the distant planet where it was banished.
To be added...
Phil Coulson, acting on a clue he believed Grant Ward had accidentally given him, ordered Leo Fitz, Jemma Simmons, Luther Banks, and two agents to investigate an abandoned Distant Star Facility. Coulson hoped that the team could discover more about HYDRA's grand plan to bring back their leader. The team reached the facility, and while Banks and the two agents explored ahead, Fitz and Simmons discussed the Monolith. Simmons expressed her belief that they could not rescue Will Daniels from Maveth as there was a chance that in doing so, they would give HYDRA's leader a chance to escape as well.
As Fitz was about to answer, a shot rang out. Banks had killed the two other agents and swiveled to point the gun at Fitz and Simmons. Fitz begged him not to kill them, but Banks managed to say that he was not controlling the gun before it floated out of his hand, turned, and shot Banks in the forehead. Giyera revealed himself as the cause of the deaths and emerged from a pipe. Giyera explained that Gideon Malick needed Fitz and Simmons, and ordered the two to follow him to HYDRA.
Once at the HYDRA base, Leo Fitz and Jemma Simmons were placed in two different rooms. Grant Ward entered the room where Fitz was being held and told him that HYDRA needed him to lead their team through the portal to Maveth. Ward told Fitz that if he refused, Simmons would be tortured. Fitz remained silent, and Ward ordered Giyera to torture Simmons, which he complied with by using his power to beat her with metal implements. Fitz sat in distress as he listened to the sounds of anguish and pain coming from Simmons' room.
Fitz finally gave in to helping HYDRA after hearing Simmons scream from being tortured. He went through the portal to Maveth to help HYDRA bring the dark Inhuman back to Earth but secretly he was hoping to bring back Will Daniels. When S.H.I.E.L.D. learned that Fitz and Simmons had been kidnapped, they went to the HYDRA Castle which led to the Attack on the HYDRA Castle.