I have decided to break this book review into two posts, partly because the book is so long it warrants a long synopsis and partly so that readers can more easily ignore the synopsis if they don't want to know the plot.
Fulgrim by Graham McNeill. Approximately 500 pages.
Laeran, the Great Crusade, c. 30,000. Ostian Delafour, sculptor, and Serena D'Angelus, painter, attend a recital by Bequa Kynska. Meanwhile, Solomon Demeter leads the 2nd company of the Emperor's Children into battle upon Atoll 19 of Laeran. The Atolls are floating coral cites that ply the skies of the ocean world. The Laer are a tough alien foe with technology matching that of the Imperium. It was recommended that Laeran be ignored because it would be a long and costly endeavour to conquer it. Fulgrim promises to take it in a month.
The Emperor's Children take Atoll 19. Delafour rejects the amorous advances of Kynska. Many more Atolls and underwater cities are captured or destroyed. The apothecary Fabius carries out autopsies of the dead aliens. He discovers that they are all different, perfectly adapted and engineered for their specific role. Fulgrim gives Fabius the opportunity to study the Laer biology with the prospect of being able to enhance the Space Marines own geneseed in a similar way.
The warrior lodge of the Emperor's Children meet in secret. Saul Tarvitz are made full captains. Fulgrim reveals that the majority of the legion will accompany the Iron Hands into the Perdus Anomaly but that a small contingent, led by Lord Commander Eidolon, will turn back to police territories already won.
The Emperor's Children launch a massive attack on the last remaining Atoll. Vairosean's company take heavy losses. Demeter's ship crashes into the ocean. The Laer ferociously defend a temple which contains a mysterious blade. Fulgrim battles into the temple and seizes the weapon.
An Iron Hands fleet hunts*, and is then ambushed by ships of the Diasporex, a conglomeration of pre Age of Strife humans and aliens. Primarch Ferrus Manus announces that the Imperial Fists have been recalled to Terra and that the Iron Hands will be reinforced by the Emperor's Children. Many remembrancers visit the Laer temple and are overcome with strange feelings. Delafour is prevented from going by Kynska. Demeter is tended by Fabius. Manus and Fulgrim meet.
Fulgrim suggests destroying the Diasporex fuel sources. Manus upsets Fulgrim by disparaging art. Eidolon provides Fabius with a secret laboratory aboard the Andronius in return for the promise that he will be the first to be enhanced. Fabius experiments with Space Marine pleasure centres, their muscle and bone properties and their metabolism. He also tries to replicate the Laer's sonic shriek.
D'Angelus begins to add her own blood to her paintings. Demeter and Vairosean spar. Vairosean is receiving a chemical stimulant from Fabius as he anxious to recover his standing following his company's failures in the final battle on Laeran. Demeter refuses to take the chemicals.
The Iron Hands find the Diasporex solar collectors and attack them. Kaesoron visits Tobias, an archivist, to learn more about the sensations he experienced in the Laer temple. Fulgrim starts to hear a voice in his head criticising Manus. Fulgrim is furious with Manus for launching the attack without him. He boards the Diasporex command vessel to claim the final glory. Demeter and the 2nd company take the bridge. Fulgrim argues with his inner voice which disparages both Demeter and Manus.
Eldrad Ulthran, Eldar Farseer, sees visions of blood, death and horror for humanity with only a tiny chance for redemption. The Emperor's Children leave the Iron Hands to explore the Perdus Anomaly. Eidolon, Lucius and Tarvitz rejoin the legion from their mission on Murder with the Luna Wolves and Blood Angels. The lodge meets again. Eidolon gives a biased account of his exploits on Murder which rankles with Tarvitz. Demeter quizzes Tarvitz who upsets Lucius.
Fulgrim explores a deserted paradise world. Aboard the Pride of the Emperor, Fulgrim's flagship, the remembrancers who visited the temple are driven to realise their frenzied visions. Fulgrim is enraged by Delafour who accuses the Primarch of creating art which is too perfect. Lucius requests to be painted by D'Angelus.
Fabius implants the Laer shriek into Eidolon. Fulgrim discovers five more deserted paradise worlds, but leaves them all without claiming them for the Emperor. Vespasian and Demeter share their doubts about the legion. D'Angelus murders another remembrancer to use his body for her painting of Fulgrim.
Eldrad meets Fulgrim on a deserted world. Eldrad warns Fulgrim of Horus' treachery. The will of the Laer sword goads Fulgrim into attacking Eldrad. Fulgrim kills an Eldar Avatar. Eldrad escapes, vowing never to trust humanity again.
An emissary from Terra informs Fulgrim that Magnus has displeased the Emperor and has been ordered back to Terra by the Space Wolves. He also tells Fulgrim that Horus has been seriously wounded and that innocent citizens were killed upon his return to his flagship. Fulgrim is instructed to remind Horus of his duties in the Great Crusade.
D'Angelus encourages Lucius to begin cutting himself. The voice in Fulgrim's head grows stronger. It tells him to side with Horus against the Emperor. Fulgrim meets Horus. With the aid of Erebus of the Word Bearers, Horus turns Fulgrim against the Emperor.
Demeter is fighting Orks upon Deep Orbital DS191. He is supposed to be relieved by Kaesoron and Vairosean. Thet do not respond. Vespasian challenges Fulgrim who murders his commander. Tarvitz rescues Demeter.
Fulgrim tries to turn Manus. The two Primarchs fight. Fulgrim defeats Manus and destroys much of the Iron Hands fleet.
Fulgrim sets off for Isstvan 3 but warp storms envelop his ships and many of his astropaths are killed. Eventually, the loyal Emperor's Children are sent to the planet's surface along with other loyal Marines of the World Eaters and Sons of Horus. They are virus bombed by the traitorous parts of each legion. Demeter, Tarvitz and Lucius survive. They help to fend off ground attacks by the traitor Marines. Demeter unwittingly helps Lucius to kill loyal Marines. Demeter is killed by the turncoat Lucius. Horus sends Fulgrim to Isstvan 5 to build a fortress.
Manus rushes to Isstvan 5. Delafour finishes his statue of the Emperor but is then murdered by Fulgrim. Lucius goes under Fabius' knife. D'Angelus finds the body of Delafour and commits suicide. Kynska stages a riotous concert for the Emperor's Children aboard the Pride of the Emperor. It's audience is overcome by sensations and begin to riot. Some of the instruments are seized and used as sonic weapons. Daemons materialise. The Astartes and remembrancers are engulfed in a maelstrom of death and debauchery.
The Iron Hands meet with the Raven Guard and Salamanders. They attack Isstvan 5 without waiting for the supporting legions. The fighting is bloody but the loyalists seem to be winning. The Night Lords, Word Bearers, Alpha Legion and Iron Warriors turn traitor and attack the loyalists who are massacred.
Fulgrim and Manus fight. Fulgrim kills Manus. Fulgrim immediately regrets his actions. In his grief he allows the daemon which was held within the Laer sword, and has been whispering in his head, to possess him.
Fulgrim presents the head of Manus to Horus. Horus makes the daemon promise to keep its possession of Fulgrim secret.
The Alpha Legion are sent to delay the Space Wolves and White Scars. The Night Lords are despatched to the Eastern Fringes to confront loyalist forge worlds. The Iron Warriors are to fight part of the Imperial Fists legion. The Sons of Horus, Emperor's Children, Deathguard, Word Bearers and World Eaters make for Terra to attack the Emperor.
*Edit for accuracy.