They also want the extra power so that it will be easier to enslave a suitable noble. With extra power, they will be able to enslave a rank 4 noble, which will make what they want to achieve even easier.
So after getting home, the first place they went to was the outer city to find the boss of a gang there to enslave. This boss will be the one to help them sell the divine flesh that they have and will also help them acquire the divine flesh that they want to use.
It is a smart thing not to sell stolen goods personally. But it is even smarter to hide their pathway from others. So enslaving someone and using that person to help them do their business while they remain in the dark is the best way to achieve these two smart things.
The outer city is a large hotpot of various ingredients. People from various walks of life enter the outer city and meet here, including the nobles.