This synopsis will contain spoilers!
Flay, the first servant of Lord Sepulchrave, the Earl of Gormenghast, visits Rottcodd in the Hall of the Bright Carvings to inform him that a son, Titus, has been born to continue to line of Groan. Rottcodd, despite hardly ever receiving visitors, does not react with much emotion, and Flay leaves annoyed, having hoped to illicit a more substantial reaction from the man. He heads down to the kitchens, where he sees the head chef Swelter and the others among his staff celebrating the birth in drunken revelry.
Flay leaves the kitchens, annoyed at Swelter, and is followed by Steerpike, a servant in the kitchens who dislikes his position there and is seeking higher station. When Flay discovers the youth following him, he is annoyed, but Steerpike charms the older servant by complaining about Swelter, who he realizes Flay despises. Flay takes Steerpike along, through the Countess’ room of cats, and to a room where they can watch the Earl speak with Doctor Prunesquallor about the new baby. The Doctor admits that the baby is the ugliest he has ever seen, and remarks upon the oddity of his violet eyes.
Flay locks Steerpike in a room and leaves him there, annoyed and embarrassed that he overheard such details. Steerpike, however, leaves the room via a window and climbs upon the castle walls. He discovers a huge flat stone structure that no one else knows of, and sees an ugly poet reciting verse in solitude. Finally, he climbs through a window in an attempt to get back into the castle.
Fuchsia, the teenage daughter of Sepulchrave, heads to her attic to obtain privacy and flee from the news of a new baby brother, which annoys her. Upon entering her private attic, she finds the body of Steerpike (who is only pretending to be asleep) laying underneath the window. She pours water from an old flower vase upon his head to revive him, but the water has gone fetid. He awakes, and begins to charm Fuchsia by regaling her about his heroic adventures upon the outside walls of the castle. She brings him down to her room.
In her room, Mrs. Slagg, Fuchsia’s and now Titus’s nurse, arrives to tell her that Dr. Prunesqallor has asked for her to visit. Steerpike convinces her to bring him along. When they meet, Prunesquallor gives Fuchsia a necklace, and Steerpike talks his way into living and working with the doctor and his sister Irma.
A wet nurse named Keda is chosen for Titus among the Mud Dwellers who live outside the castle. She lost her own baby only recently. At the christening for Titus, Flay and Swelter have an encounter in which Flay strikes Swelter and causes him to bleed. Swelter swears revenge to himself, and Flay realizes it, straining their already bad relationship even more.
After only two months, Keda comments that Titus is strong and healthy, and she returns to the Mud Dwellers where she finds the two men who loved her still waiting for her. She sleeps with one, and the other finds out. Keda claims to love them both, and they decide to duel for her love. They kill each other during the fight and Keda, disturbed, flees her home and begins a lonely journey.
Steerpike, meanwhile, meets Cora and Clarice, Sepulchrave’s twin sister. He begins to charm them, and eventually dominates them with promises of improving their station in the castle. He convinces them that in order to do so, they must burn down Sepulchrave’s library (books being the one thing he loves). Steerpike arranges everything, and on a night when everyone is within the library, the sisters set it on fire. Steerpike arrives just in time to rescue everyone except Sourdust, the old man who is responsible for ensuring all the many rituals of Gormenghast are observed.
Prunesquallor and the Countess remain wary of Steerpike and his fortuitous arrival at the fire, but do not accuse him. Barquentine, Sourdust’s son, is found and instated as the new master of rituals. One night, Flay is returning to his room and he comes across Swelter practicing sneaking up on and murdering a replica of Flay and his sleeping arrangements. He begins to lose sleep. Keda returns from her journey and is pregnant. She is nursed back to health by an unknown character and then returns to the Mud Dwellers.
The Countess catches Flay throwing one of her cats in anger, and she banishes him from the castle once the birthday celebration for Titus is complete. With the burning of his library, Sepulchrave becomes more and more mad, to the point where he becomes possessed by the spirit of an owl and begins to act like one. Prunesquallor gives him medicine to sober him up for the birthday celebration, but he goes mad again shortly afterwards. Flay leaves the castle, but returns every night so that Swelter does not realize he has been banished. One night he sees Swelter heading to kill Flay, and so Flay follows him.
Swelter discovers Flay is not there, and a bolt of lightning reveals the men to each other. Sepulchrave, sleep walking, shows up and Flay uses him as means to lead Swelter to the Spider Room where they can finish the fight. Flay is able to kill Swelter, and Sepulchrave, mad, takes Swelter to the Tower of Flints where he is killed by the owls who live there. Flay goes to live in the woods, where he, months later, witnesses Keda commit suicide after the birth of her baby.
When Sepulchrave cannot be found it is determined that Titus will become the new Earl. Steerpike helps Barquentine and becomes his assistant. Steerpike, afraid the Aunts will reveal his role in the fire, dresses up like Death and scares them into never speaking of him or the fire in public. Steerpike does not know it, but Prunesquallor does hear one comment about the fire that raises his suspicions further, and he warns Fuchsia to be wary of the young man.
A ceremony is held at the lake to make Titus the new Earl. He is less than two years old. During the ceremony he throws some of the precious items of the ritual into the lake. Across the lake, Keda’s baby (described as alabaster) struggles in the arms of the woman holding her. Titus cries out, and the baby responds.
"Gormenghast, that is, the main massing of the original stone, taken by itself would have displayed a certain ponderous architectural quality were it possible to have ignored the circumfusion of those mean dwellings that swarmed like an epidemic around its outer walls."Mervyn Peake the First Line of Titus Groan
Mervyn Peake the Last Line of in Titus Groan