what's the name of the movie where an alien arrives on earth for a while and the goes back to home planet?

please help me! I watched this movie too many years ago and I don't
remember who's staring or what's the name to find it. the only thing
I remember is that this alien looks like a human and he's staying in a
mad-house from where he's taking one of the patients with him on his
planet. oh and as I remember he's moving through the speed of light.
please help...