Hi Dee. I just replayed the game and made sure I saved Mandy this time around, but my score was much lower (34 rather than 69), so I got penalised for saving her. Any chance of giving a rundown on how the scoring works?
Incidentally, after re-reading this thread, I just tweaked to the cause of the fire. It was when Mandy discarded her cigarette butt in the bush, right?
Basically, there are three possibilities with Mandy, but it seems that nobody's found the third yet (or at least nobody's mentioned it if they have!) The first is if you never encounter the troll, and so the boss gives you each a share of the payment at the end. The second is if Mandy gets killed by the troll, so you get the whole payment (and hence a better score). The third is if Mandy gets caught by the troll and you manage to save her before it's too late.
The game is perfectly winnable with a low score, and I'd say it's (deliberately) pretty difficult to get max points, so it's more for fun than anything else! Things you might want to play around with include the rucksack, the coin and the pickaxe.
And yes, if Mandy makes it past the lake, it's her cigarette butt that causes the fire. If she doesn't, it's because you go through her rucksack and carelessly toss aside the contents, including a magnifying glass that sets fire to the grass - but a few people have mentioned they were confused by that, so again it's maybe something I need to make clearer.
