In 431 BCE, Heremos was tasked by Kleon to travel to Mytilene on the Greek island of Lesbos, seemingly to help distribute supplies to the city's citizens against their oppressors. However, while attempting to sneak out to meet with an associate,Heremos was captured by the Spartan Army who were camped outside of Athens. Heremos was subsequently taken to the Mt. Pentelikos Marble Quarry to be interrogated for more information.
Later on, the misthios Kassandra recovered a letter on a Spartan commander detailing Heremos' capture, reporting it to Kleon. In turn, the Athenian general requested Kassandra to locate and free him. However, she was too late as she found Heremos hanged from the crane in the quarry. After freeing and helping Onomakles, Kassandra reported Heremos' death and the mission to Kleon.