The Summer of the Danes is a medieval mystery novel by Ellis Peters, set in 1144. It is the eighteenth in the Cadfael Chronicles and was first published in 1991. Brother Cadfael is pleased to join his young friend Mark, now a deacon, on a mission of church diplomacy in Wales. Travelling in the safety of the Prince of Gwynedd's train, they are brought to unexpected dangers, as they seek to keep a young Welsh woman free from harm.