Witch and Mercenary novel volume 4 was written by Chohokiteki Kaeru with illustrations by Kanase Bench.

When Siasha gets called away to help someone on a job, Zig finds himself with time to kill. He's quickly recruited by Katia, the daughter of a mafia boss, to help investigate the spread of a dangerous drug across the city. Tempted by the lure of a big payout, Zig accepts the request, and together they dig into the underbelly of society... only to discover the problem runs much deeper than they expected.