Set on the Hive World of Necromunda, The Redeemer chronicles the battles of a small band of Redemptionists, fanatical and homicidal cultists of the Emperor, led by their supreme leader and arch-maniac, Klovis the Redeemer, as they fight to stop the Caller, a deadly and extremely powerful Ratskin Shaman, who is leading a horde of Ratskins, Scalies, Plague Zombies and other Underhive Scum in a revolution against the nobles of the Spire.
The first issue (Epistle) opens with the Redeemer and his maniacs purging a group of Ratskins for a crime Malakev (the narrator) cannot even say (they tried to run away).
In the second issue, the Caller gathers his armies and the Redeemer is captured by a psyker called Ferron Voor, the Emissary of Karloth Valois; Master of Plague Zombies, who drains the life from several of his men to reanimate a monstrous mutant rat, with which he tries to kill Klovis (only to die in the process).
In the third issue, Klovis and the Caller's armies finally battle with each other, the Slaught-drugged Redemptionists wreaking great havoc whilst Klovis manages, in a superhuman effort, to destroy the Rat God (from the last issue), the Bloodmare Spider Queen and the Caller, despite being badly wounded in the process.
In the end, only one survives: Malakev, who is shown on the second last page of the issue to have been converted into a Scribe-Servitor, a mindless cyborg slave who will spend the rest of his existence writing down Klovis' deeds.