The Hero of Creature of Havoc begins this adventure with no idea who they are or where they are. The player is an unidentified beast and begins the adventure with no concept of language or reason. The player must discover what has happened to them and along the way a greater plot unfolds.
Creature of Havoc begins with an extensive background section detailing the recent history of an area of Allansia known as Trolltooth Pass. An Evil Necromancer named Zharradan Marr has slowly been seizing power in the region by building up wealth and a small army. He is particularly feared as a practitioner of marrangha, a type of black magic that involves the transformation of limbs and organs from one creature to another. Marr learnt this from his mentors in the village of Dree, an evil settlement of witches.
Over the years Marr has built up a dedicated ring of followers: Vallaska Roue, a Human; Hannicus, a wizard of Neutral alignment; Thugruff, a Half-Troll; and Darramouss, an undead Half-Elf. Hannicus gives Marr much information about the area, including the legend of Stittle Woad - an Elven village in the Forest of Spiders that supposedly hold three "Vapours" - benevolent spirits which bestow the gifts of reason, languages and Elven magic.
Marr, interested in the secrets of Elven magic, manages to steal the Vapours - however, he finds that he cannot understand their secrets without finding the village of Stittle Woad. This presents a problem, as the village is hidden high in the forest's treetops by Elven magic. A solution presents itself in the form of the Galleykeep, a flying ship that arrives from the east. Marr uses his troops to capture the flying ship and makes it not only his new headquarters, but a tool to discover the location of Stittle Woad from above.
Little of the background information is relevant to the player at the beginning of the book, for they wake up in a dark corridor to find that they have no memory of who they are. Not only that, but the player is not even human - they take the role of a large, powerful and unintelligent beast.
This results in some difficulty as the player makes his way through the first sections of the book, which are set in Marr's underground dungeons. Because the creature cannot make its own decisions, it is governed by instinct, and die rolls are used to determine decisions rather than the player's own choice. This changes once the player finds the Vapour of Reason, which allows him to make his own choices.
The player proceeds through the dungeon, killing a number of adventurers which (judging from information in the background) are seeking to recover the Vapours. The player soon finds the Vapour of Languages, which allows him to understand what others are saying. Various items need to be found and places and enemies avoided to succeed. These include the pendant that locates secret passageways, a crystal club, reading the parchment divulging the existence of Marr's Netherworld portal, being showered with Elven Dust near the lair of the glistening Chattermatter (and avoiding this fiendish creature's invitation to come closer!).
He then encounters the wizard Hannicus, who has been imprisoned by Marr for incompetence. Hannicus tells the player how to get past Darramouss, who guards the exit of the dungeon. He gives the player a Ring of Holy Blessing. The player uses this information to kill Darramouss by smashing the ring against a wall, releasing a gas that is lethal to the undead Half-Elf. The player escapes via the northward secret passage that Darramouss managed to open seconds before he dies, and then informs the Human guard he encounters that the Half-Elf gave him "no signal" to leave the dungeon. The guard, incredulous, nips off to investigate, but the player must remain where he is or he will not be let through the exit door when the guard returns (in addition he must give up his pendant). The player finally leaves the complex via stairs that lead into the middle of a graveyard.
On the surface, the player investigates the old building and there is visited by the Women of Dree, who send him on a quest to find them Sculliweed root. On the way the player heads south towards Coven but does not stop there, and befriends a Half-Orc named Grog, after a Human tried to kill him after his dog was eaten by the Half-Orc. Grog directs the player westwards towards Rosina the fortune teller, who in turn directs him north towards Bu Fon Fen. The player must locate the blue-stemmed Sculliweed by taking firstly the path northwest towards the Fen (Grog warning him to avoid the centre of a muddy clearing on the way), and then a path leading north in order to investigate the plants on the riverbank, although this attracts the attention of the local Toadmen. Grog comes to the aid of the player but is in turn killed by the Toadmen. Before he is killed the Half-Orc leaps out on top of the Toadman leader, pushing him into the mud. Whilst the other Toadmen attempt a rescue, the player makes his escape, but not before gathering Grog's knapsack, which contains a wooden box.
The player delivers the Sculliweed to the witch-women, who in return tell him much about his past, present and future. They tell him to seek out the Elf, Daga Weaseltongue, but warn him that any sentence he utters that begins with a consonant is a lie. For this reason, they give the player a ring that enables him to see through Weaseltongue's lies. The Witches also transport him to the banks of the stinking Bilgewater, and there the player has to mount the Ophidiotaur he encounters by feeding it a small bird. The creature runs at high speed through Knotoak Wood to where Weaseltongue is located. After the player defeats two Brigands who were attacking the Elf, the latter tells the player how to get on-board the Galleykeep, which involves being caught in a trap, many of which are littered around the forest to provide the flying ship with food, although the player must remember to use the ring the Witches gave him. The player must stomp through the undergrowth to succesfully find a trap and trigger it only when the Galleykeep approaches, to avoid exhaustion in trying to free himself (though he needs to be Lucky to locate it). Weaseltongue also divulges that Zharradan Marr's quarters aboard the ship are marked by symbol relating to the substance "that ends the fight" when "fire meets ice" (ie. water).
Onboard the Galleykeep, the player fights past Marr's creatures and confronts the necromancer himself, through the door marked with a jug of water. Remembering what the player read on the parchment back in the dungeon, he realises that Marr is on the other side of a mirror in an unreal Netherword. Marr reveals what is inside Grog's wooden case: the Vapour of Elven Magic. He also reveals that the player was originally the Captain of the Galleykeep, and was transformed into a hideous beast using marrangha after Marr captured the ship. Many of the monsters the player killed in Marr's dungeons were former members of the crew, likewise transformed by marrangha.
Marr demands the Vapour, but the player defeats him by firstly resisting his spell through having been showered with Elven Dust, and secondly by destroying the mirror with a crystal club, banishing Marr forever to the Netherworld. With the necromancer gone, the effects of marrangha wear off, and the player reverts into his previous human self. The book ends with him returning to his position as commander of the Galleykeep. One unsuccessful ending is that the player gives the vapour to Marr, because he is unable to ward off Marr's spell that inflicts severe agony, and with that the player agrees to become Marr's new right-hand man and (in epilogue) kills Marr's previous lieutenant Vallaska Roue. Marr then uses the vapour to find Stittle Woad and takes over Titan. A third ending is that, having resisted Marr's magic, but lacking a crystal club, the player is unable to crack the mirror, Marr escapes (for now) and his minions catch up with the player and kill him outright.