It has been over a decade since the release of Warhammer 40,000: Space Marine, and that means it's potentially been nearly as long since you experienced the story. Whether you've forgotten some of the plot points or have never played the game at all, we're here to help get you caught up to speed with all of the original game's major story beats before you play Warhammer 40,000: Space Marine 2.

In the opening moments of Warhammer 40,000: Space Marine, the Forge World Graia finds itself under attack by a massive group of Orks known as a "WAAAGH," in this case led by Warboss Grimskull--with a name like that, his intentions are pretty clear, and Grimskull is specifically interested in capturing a large weapons-production facility and a large mech called a Titan Invictus. This mech happens to be the most powerful weapon on the entire planet, so it's vital that Grimskull and his Orks are stopped if they want to save it. The planet calls for assistance, with the 203rd Company of the Cadians the first to respond. Many of the reinforcements were destroyed before they could reach the surface by commandeered orbital guns, and the most famous combatants in the Imperial army--the Ultramarines--are sent in to destroy the invaders.

Captain Demetrian Titus, who is the protagonist in both the original and Space Marine 2, is joined by Veteran Sergeant Sidonus and the newcomer Leandros. The approach in a strike cruiser but, to avoid suffering the same fate as the earlier ships, they base-jump out of the vehicle and use their Jump Packs to slow their fall--Leandros isn't a fan of this plan, which technically violates the Codex Astartes, or the Marine code of conduct. However, he still participates due to his lower rank.

As they near the surface, the three Space Marines are separated. Sidonus and Leandros manage to reach Graia's surface, but Titus lands on an Ork ship. He begins slaughtering Orks and locates Warboss Grimskull but chooses to turn the ship's guns on itself rather than kill Grimskull. It may seem like certain death, but Titus survives the crash and locates Leandros, with the two later linking up with Sidonus as they battle waves of Orks. Their new mission is to save the soldiers in the Astra Militarum, otherwise known as the Imperial Guard. These soldiers are not artificially enhanced like the Space Marines and are almost certainly going to die without their assistance.

Fortunately, Titus and his small crew are successful in securing the battlefield, and they manage to locate the 203rd Cadian Regiment's last surviving Imperial Guard officer: 2nd Lieutenant Mira. However, the fight is far from over, as the crew next attacks the commandeered orbital guns and destroys them in order to prevent other ships being shot down.

Next, Titus' squad moves toward the Manufactorum, which is where the planet's Battle Titans--enormous, walking mechs--are located. However, after arriving there, the group receives a distress message from an Inquisitor named Drogan, who makes it clear that a device he is developing risks falling into the Orks' hands. The plan then shifts to rescuing Drogan before the Orks are able to find him. After arriving at Drogan's location, Titus and co. discover that the device is a hugely potent power source capable of destroying the entirety of Graia if it fell into enemy hands.

During their attempt to locate and secure the device, Titus' group is attacked by Grimskull's forces, but Titus is able to locate the device in a generator room within the Manufactorum--removing it leads to a massive explosion, but Titus survives and battles his way through waves of Xenos in order to link up with his allies.

It's here where inter-party conflict comes to a head, as Drogan has no idea how Titus was able to handle the power source without dying. It conducts raw energy from the Warp, which acts as the source for power by agents of Chaos. Leandros accuses Titus of heresy, but there is still a mission to finish, and Drogan explains that the Imperium hopes to use this device to power a weapon called the Psychic Scourge--it hasn't been tested yet, and could either eliminate all Orks on Graia or destroy the entire planet. Options are limited, so Titus suggests taking the chance.

With the airborne Ork Stormboyz in pursuit, the Ultramarines and Lieutenant Mira arrive at Drogan's research facility, where the weapon is located, and Titus fires it. However, it wasn't actually a weapon capable of destroying the Orks, but rather a way to open a Chaos portal containing demons. Drogan, as it turns out, has been dead for a very long time, and the demons' leader, Lord Nemeroth, was merely using his corpse as a puppet to trick the group into opening the portal.

Things go from bad to worse, as Titus and crew now have to contend with not just the Orks, including Grimskull, but also a horde of demons and Chaos Space Marines. The Ultramarines find they have no choice but to use the Titan Invictus in order to destroy the planet's Orbital Spire and stop the invasion of Chaos forces. Titus is stopped on his mission by Grimskull, who he finally kills before reaching the Invictus. He intentionally overpowers it using Drogan's device and cuts off the portal, but Nemeroth and his forces remain on Graia. Worse, Nemeroth has killed Sidonus, who was put in charge of the power source, and plans to use it to become an immortal Greater Demon. Titus sets out for revenge, much to Leandros' protests, and he's joined by the Ultramarines' 2nd Company and the Blood Ravens, who have arrived as reinforcements.

After using jump packs to reach Nemeroth's location, Titus is told by the demon that his connection to the Warp means he's destined to become a Chaos Space Marine himself. Titus refutes this, asserting his only destiny is to destroy the Emperor's enemies before engaging Nemeroth in a vicious battle. Making use of his Warp resistance, Titus tackles Nemeroth and lays down an absolute beating as the two plummet to the ground. Nemeroth is destroyed and, in what seems like the obvious move, Titus destroys the power source so it cannot be used by anyone else.

However, one loose end remains: Leandros. As it turns out, he was acting as an informant for the Inquisition, and he has brought Inquisitor Thrax and his Black Templars to Graia to apprehend Titus. Titus is given a choice to either surrender to Thrax or doom his fellow allies to guilt by association. He chooses the former, leaving in Thrax's custody but getting in one sick burn at Leandros on his way out. It's here where the story of Space Marine comes to a close, and we'll have to wait and see what led to Titus' return to combat in time for Space Marine 2.