My big question is why are the druids abducting/killing travelers between the towns who most likely are completely ignorant of what is going on? I agree the idea needs to be more fleshed out, particularly the magic item. What could druids want so badly if they are taught to derive almost everything from nature?
It's always fun to mix in royalty with the party, especially if one (or more) of the involved characters grow romantically attached to them, Perhaps the man in question is an old flame of the princess, but now she's fallen for the seductive ranger of the group and doesn't want to leave her side and elope with the man as she once planned to months ago?
If the princess and character are keeping their relationship secret it could create all kind of difficulties when others in the group agree to the proposed plan and try to move ahead with it.