When constructing a plot for a detective novel, nothing matters more than boundaries.

It's vital to know where the edges of the world will be and who will be allowed to come in and out once the mystery is in progress.

After all, it's no fun at all if basically anybody within a hundred mile radius of the corpse is a suspect.

Some of the most memorable and famous murder mysteries are the ones where the writer allows a distinctive

location to do this.

Think of Agatha Christie's and then there were none, with the characters marooned on a small

island off the coast of Devon.

Certain institutions and buildings can work as isolating or limiting devices too,

and I've covered a few of them in past episodes,

such as schools, snowed in country houses and trains.

Part of what makes the island setting work so well though is the absolute finality of it. Unlike with a train carriage say,

where there's always the possibility that a murderer is going to improbably swing down from

the roof, it's completely plausible to the reader that nobody can cross a turbulent

sea. But even Agatha Christie, who wasn't above repeating a plot every now and then, couldn't

keep sending characters to die on remote islands.

Luckily, there's a much more commonplace and believable version of this that works just as well. What could be a better place for a murder than a boat out at sea? Welcome to She Dunnet. I'm Caroline Crampton. This episode has a distinctly nautical flavor and before we get into it properly I want to explain

why this subject interests me so much. I grew up spending an awful lot of time on boats you

see and sailing is the reason my family is even in Britain.

In the early 1980s my South African parents built their own boat from scratch and sailed

it up the Atlantic eventually settling at first on the Isle of Shepey in the Thames Estuary, and then elsewhere in Kent, which is where I was then born and grew up.

Although nobody was ever murdered on board, thank goodness, long weekends spent sailing across the North Sea as a child and then a teenager.

Gave me a very healthy respect for the sea and a reasonable grasp of seamanship.

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