This quest is given by Juma in Stonestair Byway. You must speak Kerran to receive it.
The first order of business is to deliver a letter to Habika. Habika is nearby in Stonestair Byway, as well. Then report back to Juma.
Juma will then send you to The Serpent Sewer to kill a Murkwater Villain. He can be found near the zone in to Edgewater Drains.
After killing him return for your choice of breastplates.