Milos Vanek is an Interpol agent. He had the responsibility of tracking Amy and Dan Cahill after they stole Caravaggio's Medusa during the events of Cahills vs. Vespers. He was suspected to be Vesper Five: The Spymaster, a role actually held by his partner Luna Amato.
He captured the children in Turkey in The Dead of Night, but they later escaped with the help of Luna. He then confronted them again in the Pergamon Museum in Shatterproof, during which Amy and Dan managed to escape with the help of Jake Rosenbloom who impersonated Milos.
By the end of Shatterproof, he had ceased to be partners with Luna, as she tried to kill him but Erasmus saved him and died in the process. After that, Jonah killed Luna and with Hamilton's help got Milos out of the building before it blew up. His actions and whereabouts remains unknown after the events of Shatterproof.