The final boss of the campaign is a noble woman and you have just about 30 days to killer her. She is resistant to everything but having her skin turned to gold.
There's an implicit assumption here that may not be warranted, especially if Alan doesn't have legendary actions that let him escape on someone else's turn.
Not much in 5e. Maybe cr 3 for the whole thing. A party of lvl 1 could do it assuming they don't roll bad on saving throws for the traps. The wasp and glass part seems most dangeous. If party is likely to just bum rush it, maybe cr4 and a party of level 2