You catch your step sis masturbating when she thinks shes home alone! You actually manage to watch her without her knowing until she cums at which point she notices you standing at the door and freaks out! You turn the tables on her though and tell her you'll tell your parents that she has a sex toy in the house which she KNOWS they'll hate since hey're super religious! As such you get her to reluctantly give you a handjob for your silence!