BIONICLE Legends 6: City of the Lost

City of the Lost is the sixth Bionicle Legends book and came out in 2007.

Story
When Reysa, an Onu-Matoran, is mysteriously killed near Mahri Nui's Fields of Air, Defilak, the Le-Matoran Mahri Nui Council Leader orders a search to the Black Water to find out what's there. Kyrehx, a Ga-Matoran sentry, spots and finds a Kanohi mask, (unknowingly, the Kanohi Ignika, the Great Mask of Life). When she goes to show it to the council, she is attacked by animated air weeds by the Fields of Air near the Hydruka Pens, she is saved by Dekar, a Po-Matoran hunter. Kyrehx gives him the mask, and both of them go their separate ways, not knowing that a Squid of the Barraki Warlord Kalmah has spotted them with the mask.

Defilak, his friend Sarda, a Ta-Matoran, Gar, an Onu-Matoran and Idris, a Ga-Matoran travel in Defilak's submarine down to the Black Water. They are then attacked from all sides from an organised swarm of Takea Sharks, led by a being named Pridak. After the sub is destroyed, Pridak interrogates them, then takes Defilak, his 'meal' to tell him a tale.

Meanwhile, Kyrehx and most of the other Matoran of Mahri Nui spot thousands of Venom Eels heading towards the city and begin to attack. But before Kyrehx can launch the attack, she is taken by Carapar to Takadox. Takadox hypnotises the Ga-Matoran and forces her to tell him where the Ignika is. When Takadox hears that Kyrehx doesn't have the mask, he tells Carapar to go and tell Ehlek to stop commanding his Venom Eels to destroy the city, in case the mask is still inside the city. Dekar then finds out that the Kanohi mask he possesses is the Kanohi Ignika, Mask of Life, and realizes that it will keep healing any nearby attackers, he then decides he is going to destroy it.

Pridak tells Defilak about the League of Six Kingdoms, his and his fellow Barraki's once known armies. Kalmah and Mantax then find out that Dekar has the Ignika and begin to chase him whilst he attempts to destroy it in a nearby cave which causes the Ignika to create a guardian, a 300 foot-long Venom Eel. Carapar manages to force Ehlek to stop launching attacks on Mahri Nui in case the mask is still there. The two then meet Brutaka, a fallen Order of Mata Nui member who then commands that they take him to the Ignika or perish. Kalmah, Mantax and Pridak begin to fight the 300 foot-long Venom Eel which has destroyed part of Mahri Nui's upward pointing stone cord, and the Barraki are repeatedly being defeated but they are not going down.

Then, Brutaka, Ehlek and Carapar arrive. Ehlek and Carapar are hoping that Brutaka will rid them of their leader but Pridak suspects this and Brutaka does not. Brutaka then sees Dekar with the Mask of Life and goes over, claiming that he is an Order of Mata Nui member and Dekar needs to give the mask to him. Dekar refuses, saying 'If you were meant to have the mask, you would have found it first, wouldn't you?,' Pridak, finally annoyed, commands Kalmah's giant squid to drag Brutaka off to the Black Water. As Pridak corners Dekar and takes the Ignika, it sets off a bright light, which begins to envelop the whole of Mahri Nui.

Characters

 * Barraki - Kalmah, Takadox, Ehlek, Mantax, Pridak, Carapar
 * Matoran - Defilak, Dekar, Sarda, Reysa, Kyrehx, Gar, Idris
 * Venom Eel
 * Squid
 * Keras
 * Takea
 * Brutaka
 * Botar

Quotes

 * Pridak stood on the tower of his island fortress, looking down at his assembled army. His troops came from an endless number of places. Some were Matoran criminals, others ex-Dark Hunters seeking refuge from their former employer, and by far the majority were simply beings who did no long welcome in their homelands. They were thieves, murderers, traitors, and liars, and easily the most beautiful sight he had ever seen.

Trivia

 * Ehlek's eyes are seen as red on the cover of the book, when they are actually blue. In addition, his Squid are black, rather than yellow-orange.
 * This is the first book not to feature any Toa in it.