Monster Bogey

Dear Nose-Pickers, are you well? Good. Then come closer. For I'm about to tell you a right slimer of a tale...
In it, there's a bogey monster, two best friends, four daredevil slugs, a neighbour so wicked she'll give you the willy-willy-woo-woos and a castle with secret chambers.
Will it end happily?
No...Yes...Sorry, I don't know!
You'd better ask the cabaret-singing spider…