Plot ideas for Horus Heresy era role-play

At the start of the Heresy, the Great Crusade was still in progress. Yes, it was winding down, but there were still huge numbers of Expeditionary Fleets, many of which were heavily engaged bringing human cultures to Compliance or exterminating xenos breeds. The Consuls could be in such a situation or find themselves having to fight a battle on two fronts due to an enemy Imperial fleet translating into the system.

Many Consuls, on hearing the grim news that the fledgling Imperium is now riven by civil war and picking a side, still had to work out whether they should (or in some cases could) disengage to join the wider conflict.

Alternatively, they could be in the middle of negotiating the entry of a minor human empire/a forgeworld/knight world into the Imperium when either news of Horus’ betrayal reaches both parties or an enemy Imperial fleet translates into the system. If you’re feeling particularly sadistic, loyalist Consuls could be trying to bring a world into Compliance which is secretly devoted to one (or more in the case of the Word Bearers) of the Chaos Gods when a fleet of Astartes of the corresponding Legion turn up. In addition to fighting on two fronts, the Consuls have to face the daemons being summoned by both the human cultists and the enemy Astartes.

Many Expeditionary Fleets were made up of elements from multiple legions, creating immediate strife once Horus’s betrayal became known. Imagine an exploratory fleet comprised of two Legions, one of which has a loyalist primarch and the other a traitor. Both Consuls are loyal to the Emperor, but they have to work past their distrust once they hear of Horus’s betrayal. They also have to choose how to break the news to their men and decide what to do with those that would probably switch to the side of their traitor primarch if they could. This could lead to a cull of possible traitors by their loyalist brothers, a dark mirror of the Istvann III massacre.

A key question for the Consuls and one which will heavily shape the campaign, is whether they are making for Terra. If they are then they’ll have to maintain their supplies by seizing assets and can only deny worlds that produce material to the enemy by razing them/destroying their production facilities. The only exceptions to this rule are worlds that are capable of defending themselves against Astartes like a Forgeworld or Knight World. Even then, the Consuls may try and strip such worlds of their defences, requesting that they join their fleet. Much of the fighting will take place over the warp conduits large enough for a fleet to sail down. With so much travel in the Warp, daemonic incursions coupled with Word Bearer witchery are a good way to keep things interesting. The health of navigators and their resilience is even more critical in such a campaign and a detour to obtain more navigators to make up for casualties could lead to a desperate race to escort them out of a facility while enemy assassins are doing their best to kill them off.

There are advantages to keeping the fighting local, perhaps by deciding that the Ruinstorm in the current region of space is so severe that warp travel over long distances is impossible. The closer the action gets to Terra, the greater players will expect their actions to influence the outcome of the Heresy. However the sheer scale of the conflict makes this almost impossible to achieve. Keeping the fighting local also makes life far easier for you, the Gamemaster, as you don’t have to keep track of a massive number of factions and/or memorise the events of the Siege of Terra series. It also means you can have the Consuls take, hold or lose territory and create a lasting legacy. Whether or not their sub-sector survives to flourish after the Scouring is entirely in their hands.

Misdirection
What if the first news of the Heresy to reach the Consuls is that their own primarch (whom the players know out-of-game is loyal) has sided with Horus but it’s from a questionable source (like an Alpha Legion contingent)? For extra impact, have the campaign/story take place in your own version of the Heresy in which that primarch is a traitor. This has the benefit of taking the players out of their comfort zone – all their presumed out-of-game knowledge can’t be trusted and all bets are off. See the Dornian Heresy for an alternative version of the Heresy.

Another Alpha Legion based plot-line starts off with Astartes under the Consuls’ command committing acts of sabotage, seemingly in a fugue state. After investigation, the only obvious link between them is that they all were recruited from a nearby world that was brought into Compliance early in the Consuls’ careers. A successful search reveals that hypnotic triggers have been implanted by Alpha Legion operatives in the rest-day morning cartoons broadcast to juves. The players must then capture and interrogate one of the operatives responsible to reverse the conditioning and decide what to do with the men under their command from that world.

Logistics wins wars
Horus’s betrayal along with that of the Fabricator-General on Mars triggered a mad scrabble to secure supply lines and matériel by both traitors and loyalists. Here are some are examples of logistical assets that need to be claimed and held to be of value:

• Worlds that supply the materials used in Power Armour manufacture (e.g. ceramite)
• Recruiting worlds (both for Astartes and for human armed forces)
• Agriworlds
• Hive worlds that can supply munitions and the gear issued to Imperial Army regiments
• Fuel — both for vehicles and for spacecraft (possibly sourced from gas giants)
• Shipyards — while the Horus Heresy is too short-lived for vessels to begin and finish construction over its duration, the naval battles of the Heresy make repairing damage and refitting critical. In addition, there are vessels that were close to completion when the Heresy broke out. Holding them, while allies complete their work and working out how to obtain the necessary crew is a challenge worthy of a Legion Consul.
• Astropathic relays/ducts
• Sources of field surgeons/blood/organs

The great tithe grab
Tithes are collected periodically from Imperial worlds and the same goes for deliveries of material from Forgeworlds. As a result, knowledge of tithe schedules was incredibly precious at the onset of the Horus Heresy, with both loyalists and traitors rushing to collect worlds’ tithes before their enemies could do so. This situation and the associated intrigue lends itself well to players’ secondary human characters. Infiltrating the data banks of a sub-sector capital to gather the necessary tithe data or convincing a planetary governor that the Consul’s forces are the legitimate representatives of the Imperium are tasks that – if all goes well – need sharp wits rather than bolters.

There are also the tributes paid by worlds to seal their alliance with either side. Intercepting these, as occurred in the Xana Incursion (see The Horus Heresy Book Six - Retribution), is an effective way to rob the enemy of vital resources as well as potentially ruining potent alliances. Alternatively, the players could be in charge of negotiating treaties and have to be on the look-out for enemies seeking to ruin their carefully laid plans. There’s also the option of having both loyalist and traitor ambassadors negotiating simultaneously with a neutral party in attempt to get them to switch their alliance.

Again, players’ secondary characters are ideal for handling negotiations. This can allow the players to explore their Legion from a different angle. For example, the Night Lords must have used skilled human agents to spread word of their atrocities, despite the VIIIth Legion not being know for its spy-craft. Alternatively, you could have the players trying to stop neutral factions from learning of an atrocity intended to scare them into Dark Compliance, such as the slaughter of Forgeworld Accazzar-Beta by the Daemon Prince Doombreed after he was summoned by Horus (the events that occurred in the Dark Compliance audio drama).

Tithe schedules aren’t the only type of logistics data of use to the Legions during the Heresy. Given how slow it takes for information to reach Terra, at the time of the Heresy many star charts and warp routes, particularly those covering the areas only recently reached by the Expeditionary Fleets, would not have been centrally stored. Knowledge of these would grant their owners a massive advantage over their enemies.

Capture of enemy vessels, tanks and weapons is far preferable to their destruction, but as the Horus Heresy dragged on, the threat of metaphysical corruption became increasingly significant, made worse by the fact that many commanders, blinded by the Imperial Truth had no idea that this could be an issue at all. This could be a great way to have the Consuls and your players’ secondary characters confront the horror that is Chaos, by having to board a ship that they seized from one of the more chaotic Traitor Legions and recrewed, after their fleet lost vox-contract with it.

Xenos interference
Once the Heresy was in full swing, Imperial Consuls had to weigh up the need to contribute to the fight over who would rule the Imperium against the need for there to still be a Imperium once the dust had settled. While many xenos races had been vanquished or been reduced to licking their wounds, others such as the Dark Elder and the Slaugth were well positioned to harvest many now-undefended populations. This dilemma is more acute for Consuls belonging to more humanist legions such as the Salamanders and Blood Angels.

Here are some story ideas involving xenos:

• Both the players’ fleet and that of the enemy are unable to leave a solar system due to a strange thickness of the veil between reality and the Warp. Closer investigation reveals the issue to be caused by xenos structures on a lifeless world. A Necron Tomb World stirs and loyalist and traitors must work together or be destroyed.

• One side is attempting to frame the other for an atrocity against a minor xenos empire in an attempt to drag them into the conflict. 

• The players’ forces are engaged in a fierce battle against their Imperial enemies, when a terrifyingly powerful xenos fleet or force arrives. Do they try to negotiate a temporary truce and fight as allies of convenience against the xenos or do they do their best to disengage and leave their enemies facing the full wrath of the xenos? Remnants of the Rangdan or a Hrud migration 
are particularly appropriate, but don’t be afraid to create your own unnamed race. The key thing is that it should be horrific and utterly homicidal.
• One of the players’ agents arrives with news that a powerful xenos artefact has been found, one which could turn the course of the war in their sub-sector (or even beyond). The Tuchulcha (used by the Dark Angels to massively improve their warp travel capabilities) is a good example of this. Other possible examples include more powerful versions of Halo Devices (see Disciples of the Dark Gods, a supplement for Dark Heresy 1st edition). You could substitute the xenos artefact for something similarly powerful, but of human origin, such a vault to one of the Keys of Hel (the forbidden technologies sequestered by the Iron Hands), a secret weapons-testing research station or a facility that acts as a prison for powerful AI entities, valuable STC machines or templates, or other Dark Age technology. If the artefact messes with time, the players might hear occasional snatches of vox-traffic from past and future versions of themselves. 

In the case of the secret weapons research station, it could be home to a Mechanicum Magos working on a biological virus that can be tailored against specific Legions or a binaric script that will permanently burn out the neutral connection sockets that allow Astartes to interface with their power armour.