The letter details a contract issued by a local Baron to the adventurers slain by the goblins the party slayed. The letter describes that the Baron would like revenge on a a trio of hallfing bandits known as the Brothers Gray who slew a merchant caravan which included members of the Baron's family.
The reward will be 100gp for each of the halflings that is slain. The halflings are known to all wear distinctive signet rings. The rings should be sent to the Baron as proof.