Vermissian Black Ops - Heart: The City Beneath

Vermissian Black Ops - Heart: The City Beneath - Rules of Play says:

This sourcebook for the Heart RPG contains expanded and alternative rules for sending your undercity delvers on dangerous missions for the dark elf revolutionary front. You’ll also find information on the factions that make the Vermissian their home, details on Throne Division equipment, a guide to building operations and a line-by-line breakdown of the network.