Malleus is where Dan Abnett makes it clear that the Eisenhorn saga is not simply a highly entertaining Warhammer 40,000 detective series. It is the installment where the story grows darker, more unsettling, and considerably more interested in the price of fighting evil within a civilization that has already sacrificed much of its own humanity. Following the groundwork laid by Xenos, Malleus expands the scope of Inquisitor Gregor Eisenhorn’s world while also making its central figure far more morally complicated. The mystery is larger, the action is more openly supernatural, and the danger of Chaos feels much closer than before. More importantly, the novel begins forcing Eisenhorn to question whether the principles that have guided him are enough to survive the threats he faces.

As discussed in my review of Xenos, that earlier novel was such an effective introduction to the colossal setting of Warhammer 40,000 because it treated the universe as a place to be explored rather than a wall of lore to be memorized. It gave readers the perspective of an investigator moving through the Imperium’s strange social structures, criminal underworlds, religious institutions, and alien dangers. Malleus works especially well as the next step because it retains that accessibility while taking readers deeper into the setting’s darkest spiritual and ideological corners. Readers should still begin with Xenos, but the Eisenhorn trilogy as a whole remains one of the best ways to begin one’s journey into the massive fictional universe that is Warhammer 40,000. It proves that the franchise can support horror, crime fiction, political paranoia, occult mystery, and character tragedy just as effectively as battlefield spectacle.

Set years after the events of Xenos, Malleus finds Eisenhorn carrying the emotional and professional consequences of everything that came before. He is no longer simply the sharp, controlled, and confident Imperial investigator introduced in the first book. Time, loss, and years spent confronting horrors hidden beneath the Imperium’s rigid public order have taken their toll. Eisenhorn still believes in his duty and still possesses a strong sense of justice, but there is a growing exhaustion beneath his certainty. He has learned that the Imperium is too vast, corrupt, and fragile for justice to function in any clean or uncomplicated way. He has also learned that many enemies cannot be defeated by conventional means.

The plot begins with the kind of investigative intrigue that made Xenos so compelling, but Abnett quickly pushes the story into more dangerous territory. Eisenhorn is drawn into a conspiracy involving forbidden knowledge, hidden cult activity, old enemies, and threats that reach beyond the physical world. The story increasingly brushes against the realm of Chaos, a force that is far more insidious than a conventional military enemy. Chaos does not merely conquer territory or kill its opponents. It spreads through ambition, fear, resentment, desperation, and the belief that ordinary moral limits are unacceptable luxuries in a desperate situation. In Malleus, the greatest danger is not always a monster in a dark room or a cultist behind a mask. It is the argument that monstrous methods may be justified if they produce a necessary result.

That theme becomes even more powerful with the arrival of Cherubael, the daemonhost who becomes one of the defining and most disturbing presences in the Eisenhorn saga. Cherubael is not just an evil creature for Eisenhorn to defeat. He is a living contradiction: a being of Chaos bound into human form, capable of providing knowledge and power that could prove decisive against far greater threats. His existence immediately creates the kind of moral problem that no Inquisitor can dismiss lightly. Cherubael is useful, but he is also inherently corrupting. He is a weapon that cannot be separated from the horror of what it is.

Abnett makes Cherubael memorable because he is not written as a mindless, roaring monster. He is intelligent, articulate, mocking, and disarmingly calm. He understands human weakness and knows how to make temptation sound like logic. That quality gives him a more unnerving presence than a simple daemonic antagonist. Cherubael does not need to persuade Eisenhorn to worship Chaos. He only needs to make him consider whether he can control a dangerous resource, whether he can use forbidden power for a righteous purpose, and whether the alternative might cost even more innocent lives. In a universe where Chaos often appears through mutation, madness, ritual sacrifice, and overt possession, Cherubael represents a subtler kind of corruption: the conviction that evil can remain safely contained in the hands of a sufficiently strong and intelligent person.

Eisenhorn’s relationship with Cherubael is therefore one of the novel’s most important developments. Eisenhorn is not a reckless thrill-seeker, and he does not turn toward Radical methods because he wants power for its own sake. He understands the danger more clearly than most people could. Yet his years of experience have taught him that strict adherence to approved Imperial methods can fail when confronted with enemies who respect no rules, no laws, and no limits. The daemonhost becomes a test of whether Eisenhorn’s conviction remains rooted in principle or begins to bend around necessity. Every time he sees value in Cherubael’s power, he edges closer to a line that he once would have regarded as absolute.

That growing tension ties directly into the ideological divisions within the Inquisition. One of Malleus’ strongest qualities is that it refuses to depict the Inquisition as a single, unified force. From a distance, the Inquisition appears almost limitless in its authority. Its agents can command armies, seize resources, investigate powerful institutions, prosecute heretics, and condemn worlds in the name of humanity’s survival. But Abnett makes clear that the organization is full of competing doctrines, personal rivalries, jurisdictional disputes, and mutual suspicion. Inquisitors may share a broad mission, yet they can disagree completely on how that mission should be carried out.

The Puritan and Radical divide is especially important. Puritans believe that the Imperium must fight heresy, alien threats, and Chaos without using the weapons, knowledge, or powers of those enemies. Their position can be severe, even inflexible, but it comes from a real understanding of how corruption works in the Warhammer 40,000 universe. Chaos does not need a person to consciously embrace it in order to gain influence. A single compromise, a forbidden artifact, a dangerous ritual, or an attempt to master what should never be mastered can open the door to disaster. To a Puritan, a daemonhost such as Cherubael is not an asset. It is proof that someone has already crossed a line from which there may be no return.

Radicals take a more pragmatic and far more dangerous view. They believe that the Inquisition cannot adequately fight the galaxy’s darkest forces without studying, exploiting, or weaponizing the tools those forces use. In the abstract, there is a grim logic to that approach. If Chaos is a threat unlike any ordinary military opponent, then understanding its workings may be essential to resisting it. The trouble is that the line between studying Chaos and serving it can disappear with frightening speed. A Radical may begin by using a forbidden artifact to stop a greater evil, then justify a more serious compromise during the next emergency, and eventually become unable to see the difference between tactical necessity and personal obsession.

Eisenhorn sits uncomfortably between these positions in Malleus. He remains deeply suspicious of Chaos and possesses many instincts that could be described as Puritan. He does not romanticize the enemy or dismiss the danger of corruption. At the same time, the circumstances he faces begin pressing him toward Radical choices. Cherubael is the clearest symbol of that shift. The daemonhost embodies the seductive claim that terrible power can be harnessed responsibly if the person using it has the right intentions. Eisenhorn’s willingness to consider that possibility does not make him a straightforward villain, which is exactly why the situation works so well. His choices have reasons behind them. His decisions are understandable. They may even save lives. But the novel never lets the reader forget that understandable choices can still have horrifying consequences.

The schism between Puritans and Radicals also shows how the Inquisition’s internal divisions can hinder the work of the Ordos as much as the threats they are supposed to combat. The Inquisition exists to confront dangers that ordinary Imperial institutions cannot handle, but its members can become trapped in battles over authority, doctrine, and ideological purity. Inquisitors may distrust one another, conceal evidence, challenge a colleague’s methods, or focus so intensely on proving another agent compromised that they lose sight of the immediate threat. That infighting is especially dangerous in a universe where enemies such as Chaos actively benefit from paranoia, secrecy, pride, and division.

A Puritan can be so certain that Radical methods lead only to damnation that they fail to recognize an urgent threat until it is too late. A Radical can become so convinced that they alone are capable of responsibly wielding forbidden tools that they stop seeing their own corruption. Both sides believe they are defending humanity. Both can be right about the dangers posed by the other. And both can make the Imperium more vulnerable in the process. Abnett uses this conflict to give the setting real political and philosophical texture. The Inquisition is not merely an all-powerful secret police force with dramatic titles and unlimited permission to destroy things. It is an unstable, deeply human institution whose members are themselves vulnerable to dogma, ego, grief, obsession, and fear.

The supporting cast helps keep Malleus from becoming too relentlessly bleak. Aemos remains a valuable presence because his learning, loyalty, and history with Eisenhorn give the novel an emotional foundation. Alizabeth Bequin continues to be one of the more interesting figures in the series, not simply because of her unusual nature but because she complicates Eisenhorn’s tendency to view people through the practical lens of an investigation. Eisenhorn’s associates are not faceless retainers or disposable mission assets. They are people who have endured extraordinary dangers together, and their bonds create moments of warmth and loyalty amid the book’s Gothic horror.

Abnett also continues to excel at making the Imperium feel inhabited. The setting is famous for colossal wars, massive armies, and apocalyptic imagery, but the Eisenhorn books often work best when they explore the spaces beneath that scale. Malleus moves through worlds and institutions shaped by wealth, bureaucracy, religious repression, criminality, and desperation. It shows how ordinary citizens can live their entire lives under the shadow of enormous Imperial power without fully understanding the supernatural horrors being fought on their behalf. That ground-level perspective makes the setting’s oppressive atmosphere more convincing. The galaxy is not merely dangerous because wars are constantly happening somewhere. It is dangerous because its social systems create secrecy, inequality, fear, and countless opportunities for hidden corruption to grow.

The novel is somewhat more sprawling than Xenos. It includes a larger web of characters, conspiracies, locations, and occult ideas, which can make it feel less neatly constructed than the first book’s detective narrative. However, that expanding complexity suits the story. Eisenhorn is no longer dealing with a case that can be solved by following clues toward a single clear answer. He is moving through an environment where the truth is fragmented, alliances are unstable, and each revelation raises more questions. The disorder is part of the point. Chaos should not feel comfortably organized, and Eisenhorn’s own moral certainty becomes increasingly disordered as the novel progresses.

Abnett’s prose remains one of the great strengths of the book. He can write action with clarity and force, whether the scene involves gunfights, physical confrontations, psychic peril, or full-blown daemonic horror. Just as importantly, he knows how to make a quiet conversation threatening. Some of Malleus’ best material comes from interrogations, tense exchanges between allies, confrontations with ideological opponents, and moments where a character realizes that the person they trusted may not be what they seemed. The novel’s greatest weapon is not sheer violence, but suspense. Readers can often feel that something is wrong long before Eisenhorn fully understands what it is.

Ultimately, Malleus is an excellent middle chapter because it transforms Eisenhorn’s story from a clever Inquisitorial investigation into a more troubling moral tragedy. It raises the stakes without abandoning the human perspective that made Xenos work so well. Cherubael’s arrival gives the novel a powerful symbol of temptation and compromise, while the Puritan-Radical divide reveals that the Inquisition’s most dangerous enemies are not always found outside its walls. Eisenhorn still wants to protect humanity, and he remains brave, resourceful, and fundamentally committed to his cause. But Malleus makes an increasingly uncomfortable point: a person can begin with noble intentions and still become dangerous by deciding that only they are qualified to choose which rules no longer apply.

That is what gives the novel its lingering power. Malleus is entertaining as a mystery, action story, horror novel, and tour through the stranger side of Warhammer 40,000. But it is most compelling as a story about the cost of necessity. Eisenhorn’s enemies are terrifying, yet Abnett understands that the more frightening question is what Eisenhorn will become in order to defeat them.

Eisenhorn Saga

• Xenos