I have a rectangle in 3d space (p1, p2, p3, p4) and when the mouse rolls over it I need to calculate the exact Z of the point on the rect, given the mouse coordinates (x, y).

Would a Ray-plane intersection find the Z of the intersecting point?

Edit: Would this one-liner work? .. it returns the t value for the intersection, apparently the Z value.

 float rayPlane(vector3D planepoint, vector3D normal, vector3D origin, vector3D direction){

     return -((origin-planepoint).dot(normal))/(direction.dot(normal));
 }