I BORROWED MY FRIEND'S MARKERS AND THEY ARE MAGICAL

So I made a title page for this idea I have for a book that will never be written.

It takes place in medieval-ish times and it's about a witch and an alchemist who are sent on a quest from the king to discover the secret to immortality.

Blondie is the alchemist. His name is William.

The redhead is the witch. Her name is Rosalie.

The super pale dude is Rosalie's assistant. She raised him from the dead and now he's bound to serve her. His name is Adam.

The girl in the back with Christmas coloured clothes is a knight that the king ordered to go on the quest with them. She doesn't have a name yet.

The other girl is some random farmer they meet along the way who decides to join them on their quest because why not. Her name's Lucia.

Yeah. I have all the characters. Now I need an actual plot.