After 15 years in the Oregon State Psychiatric Hospital Cassidy (Natasha Henstridge) has been declared safe enough to be allowed to leave and live a normal life. But first thing on Cassidy's agenda is to pay her sister Jane (Kelly Rutherford) a visit as Jane has been raising her daughter Emily (Peyton List) as her own ever since she was committed for being criminally insane. Cassidy's return unsettles Jane and her attempts to warn people about Cassidy being insane appear to fall on death ears forcing Jane to take matters in to her own hands.
The law of casting can make or break a movie, take "A Sister's Nightmare" where we have Natasha Henstridge in the role of Cassidy who has been in an institution for the criminally insane. Now Henstridge, when it comes to TV movies, often plays the nice characters and to have her here cast seemingly in the role of someone with psychotic tendencies immediately raises your suspicions that all is not as it seems. Thankfully Henstridge is so good at playing it icily cool that as the story forms you are not entirely sure whether she is unhinged and a threat or whether maybe she has been wronged.
That brings me on to the mystery of "A Sister's Nightmare" and there are a few things going on. We get hints of some tragic event which lead to Cassidy ending up in a mental hospital. We have Jane hell bent on stopping Cassidy from bonding with Emily who whilst we are not told immediately is clearly Cassidy's daughter. For something a little different there is Emily's fear of water. And on top of this we have no one believing Jane when she feels Cassidy is still a danger, what is that danger and what is Jane really hiding other than Emily really being Cassidy's daughter. It is because of all this that even though you know that "A Sister's Nightmare" will end up with danger and a face off you are not entirely sure which way this will play out or at least not immediately.
Aside from that it has to be said that director Vic Sarin constantly uses Natasha Henstridge's looks, and by looks I mean her piercing eyes, as often as he can. And to be honest it works as scenes of her staring with the cold look of vengeance gives "A Sister's Nightmare" a nice slice of chilling.
What this all boils down to is that "A Sister's Nightmare" is in truth just an ordinary Lifetime movie. But it works what it has well so that whilst you can spot the plot points you are not entirely sure which way things will go when the big ending comes.