Selena and Clint have to make a decision. Derrick is blind, his corneas friend, and he can be a liability. Douglas, the boy they had rescued in Volume 2 wants to accompany them on their mission, saying he hates his mother, who is to blame for the death of his father. So when they leave Douglas follows--and they take him along. Soon, they get out for a pee break--and this is when they hear and see the military helicopter. They run for cover, though soldiers land and spot their car and shoot out the tires. Now, they have to hoof it on foot, hide in piles of dead bodies, get past a huge forest fire with the infected aflame and trying to kill them. It seems like the soldiers are capturing the infected alive, for some reason. Eventually, the group is captured and taken to a containment area where blood samples are taken to see if they are carriers of the infection. The doctor finds out that Selena is one of the "Manchester Three" and can't believe she returned to the infected UK. These soldiers are Americans and what they want is to create a "Super Soldier", since that's what the original rage virus was intended for before it contaminated the entire country. So this is the reason they want the infected captured--to weaponize the virus! And they infect the boy, Douglas, with the virus for Selena to watch...
Although it's a suitably grim took the are some funny bits, like the reason why they are taking the blind guy along, because "there are bears in the woods". Also, there's an interesting flashback of Selena, in which we find out she was married. Recommended reading if you're still waiting for the real sequel to 28 DAYS LATER.