Alonzo the Turncoat

A '"psychic" by day and a phantom thief at night.

"Psychic Alonzo", the Psychic of the Detective Agency
Given Fortis's high faith in the supernatural, infiltrating the agency as a psychic was not a difficult feat for Alonzo. Of course, he doesn't actually believe in the occult, and he often makes things up just to convince the detectives on making a certain move, though it often backfires. He's not exactly some manipulative mastermind or anything though, he's just trying to help his other boss, the Phantom Thief Onyx, with intel and means of escape from the detectives' grasps. However, he's conflicted, since he gets paid regularly, paid vacation, benefits, and other perks of a unionized workplace with the Agency, something he lacks in his phantom thief job.
Alonzo is the only one with any common sense in the Agency. He's often exasperated just by how dense Fortis can be, but he also tries to take advantage of it when he can. He does try to lend some assistance too, especially if it means wasting less time or preventing Fortis and Gilly from diving into harm's way.

"Basalt", the Phantom Thief's Lackey
At night and in the darkness, Alonzo wears his cloak inside out to reveal its true form, a long coat. Basalt is the lackey of the Great Thief Onyx, and is her assistant who tries to keep her out of danger and provide hints and physical aid when needed. Upon hearing of her noble cause to take artifacts and return them to their rightful home, he was touched and decided to dedicate himself to being her partner in crime. However, she isn't exactly the brightest either, so he's kind of conflicted on whether he wants to stick by her side or to defect fully to the Agency, so he just helps both sides instead,

Alonzo is childhood friends with Scoria, and technically works under her now along with Meenah as a phantom thief.