Complex sentence: The main plot follows Bean entrusted to unveil the priceless painting "Whistler's Mother" which had been bought by an American Art Gallery from France to return' the greatest' American painting to the US.
Split into simpler sentences: The main plot follows Bean entrusted to unveil the priceless painting "Whistler's Mother". Whilstler's Mother had been bought by an American Art Gallery from a French gallary to return'the greatest' American painting to the US.