Hope Folly (also known as Hope's Folly, after the Meldreth entrepreneur, Edwin Meredith Hope, who built it) was commandeered as a Prisoner of War camp during the Great War and a number of German prisoners were housed there from November 1917 onwards.
The picture shows a group outside Hope Folly. Some of the figures appear to be wounded; others are in nursing uniform suggesting that part of the building may have been used as a hospital but there are no known records to confirm this.
The German PoWs housed there were deployed clearing the River Mel and improving drainage.
Further information can be found on the Meldreth Local History Group's website: http://www.meldrethhistory.org.uk/page/german_prisoners_of_war_in_meldreth?path=0p4p24p109p