- Captain Marvel (Mar-Vell)
- Clay Quartermain (Final appearance)
- Abomination (Emil Blonsky) (Final appearance)
- Absorbing Man (Crusher Creel) (Final appearance)
- Blizzard (Donnie Gill) (Final appearance; dies)
- Mandrill (Jerome Beechman) (Cameo) (Final appearance)
- Whirlwind (David Cannon) (Final appearance; dies)
- Radioactive Man (Chen Lu) (Final appearance; dies)
- The Leader (Samuel Sterns) (Final appearance)
- Executioner (Skurge) (Final appearance)
- Enchantress (Amora) (Mentioned)
- Surtur (Mentioned)
- Annihilus (First and only known appearance)
Thor, Wasp, Ms. Marvel, and Captain America are escorting Whirlwind to a cell within the prison 42 via the gateway in the Baxter Building. As they escort him to his cell, the lights flicker. In the background, the Leader is ranting about voices in his head. They deposit Whirlwind in his cell, and encounter Clay Quartermain, who has been assigned to investigate the power fluctuations and the Leader's strange rants. Quartermain suggests they return to the main control room so that the prisoners won't be disturbed by their conversation.
The Leader has recently taken to ranting about something outside wanting to get in; Quartermain informs the Avengers that 42 doesn't have any external sensors because they hadn't needed them prior to this, but by using Mandroid sensors they did find a few unidentifiable blips on the sensors. Power fails again, and the emergency backup power kicks in; the prison cells are contained. Quartermain goes to investigate, accompanied by Captain America and Ms. Marvel. Down at the affected junction, they find that something has eaten through the power conduit.
Wasp and Thor investigate a scream; a S.H.I.E.L.D. agent has found the creature, who has trashed the control room, breaking the gateway controls; the door won't open until the next shift of guards arrive from the other side. The warden has been taken prisoner, and the bug is trying to escape to the outside. Before the Avengers can recover the warden, more bugs attack. As Thor and Ms. Marvel follow the escaping bugs outside, they observe that the station is under attack by a swarm of hundreds of the bugs. Trapped outside, Thor and Ms. Marvel fight the incoming swarm as the others make preparations. The doors open, revealing Thor and Ms. Marvel, who survived the first wave of the bug attackers.
The Avengers and Quartermain regroup at the control centre. Sensors have been restored, revealing a huge swarm of the bugs outside the super-prison, completely surrounding them. The bugs seem to be waiting for something. If the bugs take the station, then nothing will stop the bugs from swarming into Earth when the shift change arrives in less than an hour. Captain America stipulates that they will blow up the gateway from this side rather than allow the alien bugs to escape into Earth. In order to make their last stand, the Avengers take volunteers from the prisoners, as their lives are also at risk; the Leader, several AIM drones, the Abomination, the Radioactive Man, the Absorbing Man, Whirlwind, Blizzard, the Executioner, and Captain Marvel join the defenders.
While they prepare, Thor tells the Executioner about the Enchantress being controlled by Surtur. Thor promises that if the Executioner fights honourably here, that Thor will see that he has a chance to help Thor rescue the Enchantress. Captain America deploys the defenders, with Wasp, the Radioactive Man, and the Absorbing Man acting as a strategic reserve to cover their retreat, if necessary. The control room is the final stand, if worse comes to worst, where Ms. Marvel and the SHIELD agents will make the last defence before blowing the gateway to Earth.
The bugs arrive, swarming the defenders. Annihilus shows up, controlling the bugs with a control wand of sorts. Several AIM drones fall, as does Blizzard. The Abomination carries the stricken Leader clear. The front line falls back to the second choke point, where the Radioactive Man, Wasp, and the Absorbing Man cover their retreat to the cell block.
In the cell block, the bugs swarm the defenders in wave after wave. Captain America sends the S.H.I.E.L.D. agents to the control centre, and the Abomination and the Leader head there with them. The Avengers attack Annihilus, but are unable to damage him. In the control room, the Leader attempts to disrupt the energy shields Annihilus is using. The defenders take advantage of that to down Annihilus, and separate him from his control wand; without it, the bugs turn on Annihilus instead. The bugs flee, leaving the 42 prison heavily damaged but with the inhabitants intact. Captain America greets the S.H.I.E.L.D. shift change at the gateway. "Welcome to 42."
- The premise of this episode is based on the 1976 film and its 2005 remake Assault on Precinct 13.