Trying to get a parented object to face the direction of the mouse pointer in a perspective view.

I have been looking for a solution for a while now and they all say the same thing, I'm stuck on how to make a script that does what I want it to, i have tried using ray cast and other things but only wound up in either crashing unity or going to cry in a corner (In other words I don't have any example scripts that even slightly worked) so any help from beginning to end for this would be highly appreciated. Thanks in advance!