“ Temple of some malign being invites you warmly and offers help (curing,needed spell etc) for some minor sacrifice . Sacrifices must be everytime bigger to work - up to living inteligent creatures. Maybe you pay some other price,too...”
“ Draw the party together as debtors to the local lord, king, head of the thieves guild, or mercenary clan, who is forcing them to work together to pay off their debts.”