Agent 355 serves as Yorick Brown's bodyguard. Her name is pronounced "three fifty-five", not "three-five-five". As of yet her true name has not been revealed.

It's believed that she may have inadvertently started the plague that killed all the male mammals of her world. She was a on a mission in the nation of Jordan to save Dr. Frozan Hamad and an amulet in her possession. Dr. Hamad told her that it was a family heirloom. She mentioned that her father told her that a catastrophe likened to the Trojan War would happen if it (the Amulet)was removed from Jordan. After Dr Hamad was killed by people after the amulet, Agent 355 took the Amulet of Helene. Right as the Amulet entered Saudi Arabian airspace the plague hit.

She is part of the Culper Ring, a US government agency that can trace its origins back to American Revolutionary War.