Mutants break into Mega-City One and Dredd is there to stop them. He looks like he's having a lot of fun killing them too judging by his dialogue in the page above.
Dredd quips as he blows them away that fighting the mutants is 'just the sort of soft job a judge like him needs!'
The mutants are getting massacred by Dredd and retreat back into their territory outside the city.
Dredd is informed by Justice HQ that the mutants, The Brotherhood of Darkness, have kidnapped the Mayors son and he must follow the mutants and rescue him.
Dredd adopts a disguise. He puts on a robe, probably from one of the fallen mutants, and decides to fool his way into the Brotherhood as they trek their way outside the city.
We get our first glimpse of what lies outside Mega City One. It's an atomic wilderness. A radioactive nightmare as a result of the Atomic War.
Dredd gets his insects screwed up. In the first panel, it's a Praying Mantis and in the panel where the Brotherhood are barbqueing...it's a grasshopper, not the mantis he saw. I guess they don't teach that sort of thing at the Academy.
Dredd sees that the Mayors son isn't the only Mega City citizen the mutants have kidnapped and while the Brotherhood are feasting, he makes his move...
After getting rid of the guards he frees the Mayors son.
He's in the process of freeing the other captives when the Brotherhood spot him. He puts the lawmasters lights on full beam, temporarily blinding the mutants and throws a few flares for good measure.
Dredd makes his escape with the rescued slaves back to Mega City One.
This story is important for two reasons. One, it introduces Mutants into Dredd's world and two, the Atomic wasteland, which would later be named the Cursed Earth.
The script was written by Malcolm Shaw. Of the first fifteen Dredd stories commissioned by Mills, Shaw wrote seven of them. Of course Mills probably, heavily rewrote them...like he did with all the early scripts.