The heat of the 1976 summer lowers the levels of Caban Coch Reservoir in the Elan Valley and the submerged garden walls of Nantgwyllt mansion are revealed, as they were also in 1937 and 1947. Brothers Chris and Clive Powell, who had recently moved to Blaencwm farm, Llanwrthwl, and their fearless dog, Spark, brave the mud and explore the area where the house once stood. It was home to poet Percy Bysshe Shelley and his young wife Harriet Westbrook for a few short months in 1812.