A mans wife goes missing and he falls in love with this other gal and is going to marry her, in the mean time his daughter suspects she is not what she seems. Find out she is an alien and put the mother in a cave in a cacoon along with a few other people. And if I remember right something to do with an instrument of some sort. Any one know what this movie is called?

Stepmonster (http://www.imdb.com/title/tt0108223/)