Romance Bondage novel with a norse theme to it. Chaste Vikings and cleave gags, what more could you ask for?
https://books.google.com/books?id=SWPCBwAAQBAJ&pg=PT310&lpg=PT310&dq=gagged+avril%22captive+romance%22&source=bl&ots=QRCowmlIFa&sig=eIMl4GQw5xkERssKp-vapIRpqH8&hl=en&sa=X&ved=0CB0Q6AEwAGoVChMIjvuy8bySyAIViJiACh3oIwHt#v=onepage&q&f=false