Guigiaro, early 1970's,Maserati Khamsin
Giugiaro is right, but the Khamsin was designed by Gandini for Bertone, so it's nothing to do with the Khamsin..
is it the Maserati coupe 2+2 concept 1974?
..as this is indeed what it is!
Personally I much prefer it to the Khamsin; here's a rear view and the un-modified puzzle picture: