Mystery Plane

Hi all,
I was on a recently flying (as a passenger) on a flight frou Houston
IAH to SFO. When taxiing out for departure, my eyes were drawn to an
unusual plane. I want to find out what it was. It was unmarked, but
seemed to be a cargo plane by the boxy fuselage, and by the location
where it pulled up on the tarmac. (Cargo terminal)
It had:
A turboprop engine on each wing, graced by five-bladed propellers.
Fixed tricycle gear, the main gear having cowls that attatched to the
wing struts.
A shoulder (high) wing arrangement.
A conventional tail section.
It looked big enough to haul roughly 20-30 people, but sported no
fuselage windows.
It's "back" was sort of humped up.
Viewed directly from behind, the fuselage was a very fat 90*-angular
"box".
Stick-straight wings, like a DH-8, only not so long and skinny.

Had never seen anything like it before, so my curiosity is killing me.