Some random hooks:

1) While travelling the PC's are set upon by bandits, who they defeat only to learn that the crown hadn't been able to track them down and are duly grateful for the help and keeps the PC's in mind for further work.

Too martial? While travelling, the PC's discover that the next village on their route is totally abandoned. Everything looks fine, but a couple hundred villagers are missing. The PC's discover the horrible secret and put a stop to the cause, the crown is duly grateful and keeps the PC's in mind for further work.

2) The PC's are approached by the crown to recover holy relics, sacred to the king's faith. The McGuffins let you send them anywhere and do anything. Want a dungeon crawl? One is in a dungeon. Want a diplomatic adventure? One is owned by a neighboring king who will need persuasion or a cunning heist. Want detective work? One was stolen by pirates years ago and you'll need to discover what became of the crew and where the treasure is buried. Want exploration? One was taken by a missionary priest into the back beyond to preach to the heathens and has never heard from again. Want romance? A wealthy merchant will give his up, but not for money (he has plenty of that) he wants his daughter married into the aristocracy. Etc...

McGuffins (or "plot tokens" as my wife calls them) are cliche, but for a very good reason, they're super useful.

3) The PC's, now trusted servants, are offered knighthoods to track down and capture or kill a traitor to the throne, a renegade priest turned to devil worship. Nope, he's a loyal priest who has worked out who the Queen really is, and what the artifacts really do, and is running for his life.

4) After refusing to kill the priest, the PC's are on the run now too. The priest is now your source of adventures. He has a list of plot tokens he needs to identify the Queen's true form. Steal a document. Gain access to a library. Rescue a scholar.

5) Sounds like an adventure to me. Super weapon in hand, queen finally in sight, have fun storming the castle!