The Attack on the HYDRA Castle was a battle between S.H.I.E.L.D. and the HYDRA forces led by Gideon Malick. Though S.H.I.E.L.D. seemingly ruined HYDRA's Project Distant Star Return, Hive secretly managed to return to Earth.
The HYDRA Castle was built with a system that amplified soundwaves and vibrations so that the Monolith could be transformed to a portal to send HYDRA operatives through to Maveth, the place of banishment for Hive, the Inhuman worshiped and revered by the organization. For centuries, HYDRA sought a way to retrieve It from the planet but their efforts were unfruitful; however, it was learned that the S.H.I.E.L.D. scientist Jemma Simmons successfully returned from Maveth with the help of Leo Fitz. HYDRA had Fitz and Simmons abducted in order to learn how this was achieved.
Seeking revenge on Grant Ward for the Assassination of Rosalind Price, Phil Coulson traced his location to the HYDRA Castle after kidnapping his brother Thomas Ward and threatening to execute him, causing Grant Ward to stay on the phone long enough to be discovered. Coulson jumped through the portal created by the Monolith fragments after seeing Ward enter. Prior to entering the portal, Coulson made Alphonso Mackenzie director of S.H.I.E.L.D.; Mackenzie activated the Caterpillars program so that the Secret Warriors could assist S.H.I.E.L.D. in the attack.
Ward entered the portal with Fitz captive on the order of Gideon Malick, who revealed the true origin and purpose of HYDRA and convinced Ward that helping to retrieve It should be a part of his campaign. Fitz agreed to enter to stop the harm that the telekinetic Giyera was causing Simmons.Andrew Garner went through Terrigenesis and became the Inhuman killer dubbed Lash; eventually, he was captured and contained within a Containment Module. The module was shipped by Malick to the HYDRA Castle, with other Inhumans contained in Suspension Gel, as part of an army Malick was preparing for Its arrival, so that the Dark Inhuman could lead them.
Once Gideon Malick took possession of the abandoned castle which was used by the ancient HYDRA society in the 19th century, he was ready to launch the final phase of Project Distant Star Return-the opening of a portal to the planet Maveth and the bringing of the ancient Inhuman back to Earth, sending Grant Ward, Leo Fitz and a small team on the seemingly impossible mission to find It.
Daisy Johnson and Melinda May led the Secret Warriors into the base and sabotaged HYDRA's main power stations. When Giyera attempted to assassinate Johnson, she was saved by Joey Gutierrez who melted the bullets before Lincoln Campbell defeated Giyera with a bolt of lightning. Meanwhile Alphonso Mackenzie led Lance Hunter and Bobbi Morse through the Castle where they successfully took control over the portal chamber and reclaimed the Monolith fragments, creating a barricade with Gutierrez's help to keep Malick's forces out while they waited for Phil Coulson to return from Maveth with Leo Fitz and Will Daniels.
Jemma Simmons was able to escape from HYDRA's custody during the battle and attempted to find a way to freedom. While hiding from Malick's soldiers, she discovered his shipments of Inhumans that had been stockpiled by the ATCU; she also found S.H.I.E.L.D.'s Containment Module which held Andrew Garner. With HYDRA soldiers approaching, Simmons was left with no choice but to free Garner, who transformed into Lash and slaughtered both the soldiers and the captured Inhumans.
Due to S.H.I.E.L.D.'s interference, the entire team that was sent on Maveth was lost, their leader Grant Ward was killed, the Inhumans collected earlier by the ATCU were all killed causing Malick to retreat. Alphonso Mackenzie ordered his team to leave the castle while he and Daisy Johnson waited for Coulson's return. Eventually Coulson and Fitz returned alone, as Will Daniels had been killed by Hive and once they had escaped using the Containment Module, the castle was destroyed along with the portal.
- "Well I'll be damned."
- ―Gideon Malick
Hive was able to escape the destruction of the HYDRA Castle in the corpse of Grant Ward and return to Earth. Taking Phil Coulson's Prosthetic Hand, which was used to kill Ward, It managed to meet with Gideon Malick who also escaped and was driving towards an airport to escape capture. Malick was shocked and delighted that his ultimate goal had been successful.