The Renegade Shadowscale

Teinaava will tell you of a former Dark Brotherhood hatchling that committed treason against the Brotherhood and needs to be killed. When you find the argonian in the swamp, he will offer you a share of loot if you don't kill him, and instead take the heart of a dead argonian nearby. The loot available is 200 gold and you will recieve the same reward from Teinaava either way.