In Malaysia, Yelena Belova destroys a lab tied to the O.X.E. Group’s Sentry project, aiding CIA director Valentina de Fontaine, who’s facing impeachment. De Fontaine sends Belova, John Walker, Ghost, and Taskmaster to a covert facility, intending to eliminate them. Ghost kills Taskmaster, and a mysterious survivor named Bob helps the others escape.
Realizing they were set up, the group flees with help from Alexei Shostakov, who dubs them the Thunderbolts. Bob is captured and taken to the former Avengers Tower, now the “Watchtower.” Bucky Barnes intercepts the Thunderbolts and, upon learning about Bob’s transformation into the superhuman Sentry, joins them to stop de Fontaine.
At the Watchtower, the Sentry, corrupted by power, turns on de Fontaine. Her assistant activates a kill switch, releasing the Sentry’s darker alter ego—the Void—who engulfs New York in supernatural darkness. Belova enters the shadow realm to reach Bob’s mind. With the Thunderbolts’ support, Bob overcomes the Void, restoring peace.
Though de Fontaine is exposed, she manipulates public opinion and rebrands the Thunderbolts as the “New Avengers.” In a post-credits scene, they receive a distress signal from an interdimensional spacecraft marked with a “4.”