Mariah

Mariah was a converted London taxi owned by Darius Pike. She stayed in the garage and was under almost constant maintenance by Darius. (TV: Regeneration)

Features
Mariah could communicate in a feminine voice, operate under a voice recognition system, and move without a driver. She wanted Darius to clear out junk food wrappers from the back seat. (TV: Dream-Eaters, Curse of Anubis)

History
Darius and Starkey drove in Mariah on their way to Dauntless Prison. (TV: Liberation)

When Drake tried to frame K9 Mark 2, he had K9's duplicate severely damage Mariah at night. This made Darius furious, but when a CCPC grabbed Jorjie, he sided with K9. (TV: Jaws of Orthrus)

One night, Darius slept inside Mariah. In a dream induced by the Bodach, he was surrounded by clowns inside the car. He begged Mariah to open the door but she said she couldn't do that; their destination was the circus. (TV: Drema-Eaters)

When Darius was banished from the Gryffen Manor, he drove off in Mariah. When the Anubian Geb tried to hypnotise him, Mariah knocked him out by opening her door in his face. (TV: Curse of Anubis)

Darius used Mariah to drive Birdie to a safe place. (TV: Mutant Copper)

When Darius was affected by news of the Last Precinct, Mariah comforted him. (TV: The Last Precinct)

Darius was sleeping inside Mariah when Thorne came to him. (TV: Hound of the Korven)

Behind the scenes
William Pike also owned a cab which appeared identical to Mariah in The Cambridge Spy, but was never identified as being the same cab in-narrative. The official K9 site, which this wiki doesn't consider a valid source, states that she was a converted ancient cab.