Val McDermid, Scotland's bestselling crime novelist, and her partner Jo Sharp, Scotland's first female Geographer Royal, have co-written This Door of the Seas, a novella published next week that marks their first joint literary project despite having deliberately kept their work separate throughout their 13-year relationship. The book fictionalises the 1698 Darien scheme, in which more than 2,000 Scots set out to found a trading colony in modern-day Panama, an expedition whose catastrophic failure bankrupted Scotland and helped pave the way for the 1707 union with England.

The project began when Sharp, researching a book festival talk on the history of Scottish geography, uncovered the story of the first Geographer Royal and his role in monitoring the doomed venture. Both women say they were keen not to soften or "whitewash" Scotland's complicity in empire and the slave trade that followed the union, wanting the novella to acknowledge this uncomfortable history honestly. McDermid, author of 51 books translated into more than 40 languages and sold in excess of 20m copies, and Sharp, a professor of geography at St Andrews and Royal Society of Edinburgh member, describe having been wary of collaborating professionally for fear it might strain their personal relationship.