After a bumpy landing in the disco decade, the team – Daniel Sousa in tow – reunites with more than one familiar face at the S.H.I.E.L.D. hangout and discovers exactly how to dismantle the Chronicoms’ latest plan. But when they get too close for comfort, the Zephyr unexpectedly leaps forward again, this time to a date pivotal to not only the future of S.H.I.E.L.D. but to the future of Director Mack as well.
Having arrived into the 1970s, Daniel Sousa takes Phil Coulson, Daisy Johnson and Melinda May to The Krazy Kanoe, which is supposed to be a S.H.I.E.L.D. safehouse. Blending in as much as they can, with May quite struggling with her empathic abilities, they are unable to find Enoch. However, they quickly discover an anomaly in the timeline: Wilfred Malick is still alive. Under his influence, the HYDRA infiltration within S.H.I.E.L.D. has progressed much faster than originally, with Project Insight being already highly advanced.
The S.H.I.E.L.D. agents try to know more about Project Insight: May subtly interrogates General Rick Stoner and learns that the project will be completed in three years; Johnson is approached by Gideon Malick, but the conversation is interrupted by Sousa; and Coulson informs Jemma Simmons and Deke Shaw, who have remained in the Zephyr One. Shaw is extremely distressed upon learning that Malick is still alive and advocates to take him out as quick as possible.
Johnson and Sousa manage to infiltrate the room in The Krazy Kanoe from which Project Insight is managed, retrieving the list of Insight targets, which includes S.H.I.E.L.D. assets such as Bruce Banner or Victoria Hand. As it becomes clearer that the Chronicoms are involved, S.H.I.E.L.D. decides to leave and regroup, but are ambushed by a group of Hunters led by Luke, who has allied with Malick. Nevertheless, the team is able to escape thanks to Johnson taking Malick's second son Nathaniel hostage.
Fearing for his son's life, Malick agrees to let S.H.I.E.L.D. go, which greatly upsets Luke. Upon S.H.I.E.L.D.'s escape, Nathaniel witnesses Johnson's Inhuman abilities. The team is then found by Enoch, who drives a car to The Krazy Kanoe and helps them escape. Meanwhile, Alphonso Mackenzie and Yo-Yo Rodriguez travel to the Lighthouse to assess the place, hoping to find a location to establish temporary headquarters. However, they find out that the Lighthouse is active in this timeline, as it actually is Project Insight's main base of operations.
The team gathers on Zephyr One to discuss their next move. However, another time jump occurs before Rodriguez is able to use her speed to prevent the plane from time traveling, causing the team to arrive in 1976, on the day of Project Insight's launch. Sousa grows increasingly upset that S.H.I.E.L.D. is unable to control their time jumps, but is calmed down by Shaw. S.H.I.E.L.D. decides to infiltrate into the Lighthouse and cause an evacuation to prevent the launch, with Johnson and Sousa being tasked with hacking into the surveillance system to assess the presence of prisoners, while Rodriguez and Shaw are sent to find Malick.
Malick meets with Luke, who reminds him of the choice he made three years earlier: giving up on his advantage over S.H.I.E.L.D. to save someone of his family. Having learned from that, Luke gives Malick pictures of Mackenzie's parents being imprisoned in the Lighthouse. Meanwhile, S.H.I.E.L.D begin their infiltration, but although Johnson and Sousa are initially able to help Coulson and May walk through the base, they are incapacitated and kidnapped by Nathaniel, who wants to experiment on them.
Left with no other option, Coulson and May try to convince Stoner, who is still a loyal S.H.I.E.L.D. agent, of the reality of the Chronicom Hunters, but he remains unconvinced, forcing May to knock him unconscious. As Project Insight is on the verge of being launched, Coulson and May plant explosives in the Lighthouse while Shaw and Rodriguez meet with Malick, but he remains defiant and claims that S.H.I.E.L.D. will never win since Sibyl predicted their every move. Angered by Malick's confidence and still upset by what he suffered at his hands, Shaw shoots and kills him.
Eventually, through Luke's pictures and surveillance footage, S.H.I.E.L.D. discovers the presence of Mackenzie's parents being held captive in the Lighthouse, which means that they would die if the base was flooded as planned. Unable to bear the weight of his parents' death, Mackenzie aborts the operation, and May and Coulson are arrested. Despite this setback, the team cannot allow Project Insight to go through. Therefore, Mackenzie orders that the Zephyr One be taken into the air, so they can fire a missile which destroys the Insight rocket, but at a significant cost: S.H.I.E.L.D. revealed their position to the Chronicom Hunters.
- Clark Gregg as Phil Coulson
- Ming-Na Wen as Melinda May
- Chloe Bennet as Daisy Johnson/Quake
- Elizabeth Henstridge as Jemma Simmons
- Henry Simmons as Alphonso Mackenzie
- Natalia Cordova-Buckley as Yo-Yo Rodriguez
- Jeff Ward as Deke Shaw
- Joel Stoffer as Enoch
- Tobias Jelinek as Luke
- Thomas E. Sullivan as Nathaniel Malick
- Neal Bledsoe as Wilfred Malick
- Dawan Owens as Agent Ford
- Cameron Palatas as Gideon Malick
- Sedale Threatt Jr. as John Mackenzie/Chronicom
- Paulina Bugembe as Lilla Mackenzie/Chronicom
- Patrick Warburton as General Rick Stoner
- Enver Gjokaj as Agent Daniel Sousa
- Ryan Gray as Abel (uncredited)
- New York City, New York
- Lake Ontario, New York
- River's End, New York
- War Against the Chronicoms
- HYDRA Uprising (mentioned)
- Bendeery English Ale
- Yo-Yo Rodriguez' Prosthetic Arms
- Chronicom Pistol
- Chronicom Rifle
- A History of S.H.I.E.L.D. (mentioned)
- Super Soldier Serum (indirectly mentioned)
- Roger Dooley
- Leo Fitz
- Alya Shaw
- Project Insight's Target List
- Ben Taylor
- Andrew Nelson
- Susan Morse
- James Cook
- Isabelle Hartley
- Mark Roberts
- Ronald Collins
- Susan Parker
- Natahn Bowen
- Gabe Jones
- Conrad Murphy
- Bruce Banner
- Victoria Hand
- Ben Harris
- Betty Wright
- Nicoole Amador
- Michael Phillips
- Roger Stewart
- Margaret Nelson
- Leonard Torres
- Jim Morita
- Robert Gonzales
- Robert Moore
- Thomas Hall
- David Robinson
- Nick Fury
- Peggy Carter
- Sarge (indirectly mentioned)
- Phil Coulson (indirectly mentioned)
- John Mackenzie / John Mackenzie
- Lilla Mackenzie / Lilla Mackenzie
- Daniel Whitehall
- James Bond
- The Carpenters
- Mein Kampf
- A Trout in the Milk is the first episode of Agents of S.H.I.E.L.D. that depicts a full intro with the main cast being presented individually, albeit in '70s style intro, as well as the first episode to have its own title shown onscreen. The intro is patterned after the opening credits of series produced by Quinn Martin that featured a narrator reciting the cast names and episode title. Most of the footage used in the intro comes from earlier seasons of the series.
- The term "a trout in the milk" means that while there is no direct evidence of the act, there is circumstantial evidence to believe that it was the case. The phrase is said several times by Daniel Sousa, who is unaware that the phrase has fallen out of style.
- Melinda May uses the alias Chastity McBryde. In the comics, McBryde was a S.H.I.E.L.D. agent tasked with apprehending Elektra.
- Enoch's line "Come with me, if you want to continue to exist!" is a riff on "Come with me, if you want to live!" from the Terminator franchise.
- The S.H.I.E.L.D. uniforms seen in 1976 are reminiscent of the classic costumes from the comics (blue with white accents).