Abarth
Abarth is an Outsider mentioned once in Preamble. When an Annex vendor protests the inflexibility of a couple of Marcus’ goons who are shaking him down for protection money, one of the goons says,
“… or you can wait for Abarth to show up. See if the curs take city vouchers.”
Though we don’t know anything about him or the specifics of his relationship to Marcus at this point, avoiding a visit from Abarth is clearly an incentive to find a way to pay the local slumlord.
At the end of Interlocation, the Hangman’s Horde is razing Ricky’s slum. When he is discovered, Ricky asks to negotiate with Abarth, suspecting this is his gang coming to collect - or deliver punishment for - a late payment to Marcus.
Hank corrects Ricky’s confusion but shows gratitude to Ricky for confirming the names of Abarth and Marcus.