What is your characters motivation?
For some reason you agreed to collect the keys for the professor, but why?
broke and needs the money in a bad way?
wants to help people by saving them from ancient horrors?
want to help yourself by saving the world from ancient horrors?
treasures greater than money?
on the run from the law?
is the professor blackmailing you?
are you compelled to go from a deep inner voice you cannot explain?
a need for vengeance?