Complex sentence: Shane disheartedly returns to the gala and gives the watch back to the city manager Corbin Sellars, but notices it is a "BOUTINE" brand; the same brand used to start the mill fire.
Split into simpler sentences: Shane disheartedly returns to the gala and gives the watch back to the city manager Corbin Sellars. He notices that it says "BOUTINE" on it, which is revealed to be the same brand used to start the mill fire.