Not so much a memory as this is really from the history books (quite literally) Its one of those things I'd forgotten but today I had my memory jogged reading about this story.
On Google books there is "The History of the county of Lincoln from the earliest period to the present time" published in 1834 if I can read my roman numerals correctly. On page 154 talking about Mablethorpe Hall it states...
"There is a tradition, yet current, that in ancient times a French ship arrived on the coast and landed a party of men who in the night made a rapid march to this hall, and having felled a tree to enable them to pass the moat, suddenly siezed and carried off the heir to the estate, and well knowing the value of their prisoner, forced so large a ransom that a great part of the family estates in this parish and in Withern and Stain were sold on the occasion."
Food for thought...
Ian