Leo Fitz sends D.W.A.R.F.s in the storage room of the Lighthouse where the Kree Orb exploded and destroyed the three Monoliths, but the drones end up destroyed. Meanwhile, Daisy Johnson and Deke Shaw gather medical supplies for Yo-Yo Rodriguez, who tells Alphonso Mackenzie that she intends to remain and fight, despite the loss of her arms. Johnson and Shaw are attacked by a Kree Warrior who nearly kills Shaw before being shot by Johnson and vanishing in the air.
Johnson and Shaw report the attack to their friends and Fitz hypothesizes that the destruction of the three Monoliths caused the creation of a space-time rift opening onto what Fitz calls the Fear Dimension, which taps in their minds to physically manifest their fears: the Kree Warrior, but also illusions of Lash and a subterranean forest which frightens Shaw. Fitz uses Shaw's Gravity Puck to create a Gravity Containment Device which can close the rift. However, the plan requires someone to be ready to sacrifice himself and Phil Coulson offers to be the one.
Johnson, Melinda May and Fitz oppose to the idea of sending Coulson, claiming that they all need him. While Fitz suggests to send Piper and Johnson offers to go herself, Coulson refuses both the propositions, assuming that S.H.I.E.L.D. needs Johnson. A furious argument erupts as Johnson states that S.H.I.E.L.D. no longer exists and that she is the only one who can do the mission. Coulson tries to reply, but he faints due to a sudden respiratory distress. As he regains consciousness, he gives instructions to Shaw who leaves the Lighthouse, and goes to find his friends. Upon getting out, Shaw spots the military as General Hale journeyed to River's End since Johnson was reported by Officer Kennedy.
Coulson reveals the consequences of the deal he made with the Spirit of Vengeance to defeat Aida: the demonic being possession cancelled the effects of the GH.325 which had repaired Coulson's damaged tissue in the heart and lungs. As a result, the tissue went necrotic and the necrosis spreads, meaning Coulson is dying. Infuriated and overrun with grief, Johnson leaves the place while May blames Coulson for not having disclosed his condition earlier. Coulson goes to find Johnson and the two have an emotional moment with Johnson telling Coulson that he is everything she believes in. Both of them embrace as Johnson cries.
Rodriguez is attacked by another illusion in the form of a LMD of Simmons, which is destroyed by the real Simmons as it tried to smother Rodriguez with a pillow. Figuring out that the Fear Dimension is expanding and that they are running out of time, Coulson confirms his intent to do the mission after a talk with May. Fitz gives Coulson the Gravity Containment Device along with a gun, and Coulson has Fitz promising that whatever happens, Fitz and Simmons will marry as this will give hope and happiness to the others.
Coulson takes the elevator down to the deepest levels of the Lighthouse, where he encounters an illusion of Mike Peterson. Peterson assumes that he is not hostile and that he will not try anything to stop Coulson. However, Peterson also hints that Coulson is still on the operation table while being resurrected and that everything he thought had happened, from the creation of his team to the events in year 2091, is made up by Coulson's mind from his memories, his regrets and the surgeries performed on him.
Peterson seems to convince Coulson and begins taking him to the space-time rift. However, Coulson eventually stops and claims that he does not believe Peterson. The illusion gets angry and intends to force Coulson to cross the rift, but it is destroyed by the real Deathlok, who has been brought to the Lighthouse along with other S.H.I.E.L.D. agents gathered by Shaw.
Coulson and Deathlok fight several other illusions from the Fear Dimension: Lash, the Vrellnexians and Hive, all of which are destroyed by their combined efforts. In the end, Coulson activates the Gravity Containment Device, which successfully closes the space-time rift, enabling Coulson to return to his friends unscathed.
Following this success, all the S.H.I.E.L.D. agents, including the reinforcements found by Shaw, meet at the underground forest created out of Shaw's mind. Coulson and Shaw accompany Fitz to his wedding with Simmons. Fitz and Simmons exchange their wedding vows in which they express their eternal love and their happiness of having found each other and they are finally married with their friends cheering after all the ordeals their relationship had to overcome. During the ceremony, Shaw informs Deathlok that the ring Simmons is wearing looks exactly like the one his mother used to wear and which came from his grandmother, unaware that Fitz and Simmons actually are his grandparents. At the same time, Hale discovers that Shaw's DNA matches with Fitz's and Simmons'.
- Clark Gregg as Phil Coulson
- Ming-Na Wen as Melinda May
- Chloe Bennet as Daisy Johnson/Quake
- Iain De Caestecker as Leo Fitz
- Elizabeth Henstridge as Jemma Simmons/Jemma Simmons (Life-Model Decoy) (Fear Dimension's Illusion)
- Henry Simmons as Alphonso Mackenzie
- Natalia Cordova-Buckley as Yo-Yo Rodriguez
- J. August Richards as Mike Peterson/Deathlok/Mike Peterson (Fear Dimension's Illusion)
- Jeff Ward as Deke Shaw
- Catherine Dent as General Hale
- Max Osinski as Agent Davis
- Stewart Skelton as Chief C. Wellins
- Shontae Saldana as Candice Lee
- Unknown as Kree Warrior (Fear Dimension's Illusion)
- Unknown as Lash (Fear Dimension's Illusion)
- Unknown as Hive (Fear Dimension's Illusion)
- Lake Ontario, New York
- River's End, New York
- Fear Dimension
- Seattle, Washington (flashback)
- Saint Agnes Orphanage (mentioned)
- Malta (mentioned)
- Puerto Rico (mentioned)
- Maveth (mentioned)
- Closure of the Fear Dimension's Rift
- Attack on the Helicarrier (mentioned)
- Resurrection of Phil Coulson (mentioned)
- Rescue of Joey Gutierrez (flashback)
- Infiltration into Ian Quinn's Mansion (indirectly mentioned)
- Battle for the Kree City (indirectly mentioned)
- Battle of Maveth (indirectly mentioned)
- Ambush on Aida (indirectly mentioned)
- Phil Coulson's Prosthetic Hand
- Gravity Puck
- Gravity Containment Device
- Backscatter X-Ray Eye Implant
- Centipede Device
- Cybertek Prosthetic Leg
- Forearm Rocket Launcher
- Kree Battle Axe (illusion)
- Quake Gauntlets (flashback)
- Black Monolith (mentioned)
- White Monolith (mentioned)
- Grey Monolith (mentioned)
- Kree Orb (mentioned)
- GH.325 (mentioned)
- Framework (mentioned)
- Scepter (mentioned)
- Haig (mentioned)
- Vrellnexians (Illusion)
- Deke Shaw's Mother
- Ghost Rider
- A. Kennedy
- Tony Stark
- Robert Coulson
- Grant Ward (flashback)
- Thor (action figure)
- Hawkeye (action figure)
- Project T.A.H.I.T.I.
- Stay Puft Marshmallow Man
- The illusion of Mike Peterson suggests to Phil Coulson that everything he has experienced over the course of the series is a falsehood his mind has created on his deathbed. Joss Whedon jokingly made a similar suggestion in an interview with IGN in 2015 while promoting Avengers: Age of Ultron.