Billie Heck said that Hellions had stolen some crates of goods from a Family warehouse, and that it's a good opportunity to gain favor with the Family. You proceeded to take out the entire Hellion hideout, only to discover there were no actual Family goods anywhere.
Billie came clean and admitted that the Hellions were after him for stealing a magical artifact from them. Billie decided to make a deal with you: take out the Hellion bosses and he'd give you the artifact he stole. After assaulting the main Hellion base, you discovered that the Hellions had called upon the help of one of their heavies known as 3K Kelvin, who was en route to Port Oakes. Billie was unwilling to give up the artifact until 3K Kelvin was taken down.
You proceeded to the base that 3K Kelvin had taken over, and managed to overcome him and his crew. In the end, Billie made good on his deal, giving you the promised magical artifact.