An update on Milly and Felix's brief career as detectives:
There was death, labyrinth 'fun', spells IN THE WALLS, a near shave with a river and Mehitabel (the unexpected edition to the team) ended up fired from her governess job.
So... it's probably best they hang up their deerstalker hats. To be fair though Florian was found and returned to his parents, which was, after all, the major objective. Maybe we could call this interlude a partial success?
Felix and Milly never asked to be detectives anyway :P.