Complex sentence: On 13 December 1955 he was drinking and playing poker in a pub not far from his home in Newtownards, then left and went on to a friend's house where he drank some more.
Split into simpler sentences: On 13 December 1955, he had been drinking and playing poker in a pub not far from his home in Newtownards. He later left, and went on to a friend's house where he drank some more.