Denys is the second born son of Lord Ryman Mertyns. His twin brother, Peter Mertyns, is the heir to house Mertyns. They keep their seat at mistwood.
Denys rode to join Uthor Dondarrion after the murder of his son at the hands of Alyn Connington. After war was declared he was betrothed to Uthor's youngest daughter, Ashara Dondarrion.