Master Deimos is the apparent head and public face for the Hooded Wings guild, though he seems to leaves daily assignments to Grimm. He can be found on the balcony of their guildhall in the Outer City. Scarlett should see Master Deimos about joining the Wings.
Master Deimos sells potions as well: Health Potion, Mental Energy Potion, and especially the Storm Potion, which temporarily increases running speed, enabling faster deliveries.
Master Deimos also converts herbs into potions: Dusk Whin into Health Potions and White Ivy into Mental Health Potions (Note that Scarlett can make these potions, too, provided she has the Alchemy skill and the necessary Alchemy Phial)
Master Deimos offers to pay a good price for some herbs. In fact, he pays twice the going rate for Dusk Whin and White Ivy, which he uses to make Health Potions and Mental Energy Potions, respectively. He also pays twice the going rate, that is, 40 ducats each, for freshly harvested Stone Lillies, although these are not usable for potions.
Note: Stone Lillies can be a good source of cash in the early stages of the Venice chapter. Collecting 8-10 Stone Lillies from near the Canal (or easily 20-30 if the Catacombs are included) should not be difficult. Master Deimos would pay 320-400 ducats (800 to 1200 ducats for 20-30), and Scarlett could easily buy food that restores the same amount of health, but costs a fraction of the price. There is even one spot right in front of Master Deimos' guild hall where the Stone Lilly grows back regularly.