Dilos suspects it is his neighbor Bala. You go over to her house and see that there appears to be a potion there in a locked room. Bala claims she hasn't stolen anything.
If you go outside and enter Bala's house through the side you can enter the locked room from a different entrance. Pick up the potion and return to Dilos.
Talk to Dilos again to receive 10 Pix for the help.