The Stepdaughter shares several elements with another made-for-tv potboiler called Bloodknot (which sounds like a Steven Segal flick but is instead a Margot Kidder flick). I must admit my morbid curiosity about its resemblance to Bloodknot heavily influenced my decision to watch it. It's as if the writers decided Bloodknot needed a rehash except without all the mystery and (spoiler alert) incest. They also decided a younger brother with a learning disability would add gravitas (spoiler alert #2: it doesn't). And for some reason (spoiler alert #3), they decided to kill off the mom about 2/3 of the way through so they could focus more on the horribly boring investigation conducted by the sister (whose role was filled in Bloodknot by the girlfriend).
The acting is pretty ok, especially the lead who is sort of a Naomi Watts with perenially clenched teeth.
Overall, I would've given more stars if the second half had matched the first in pacing, mystery, and hamminess.