This will be lost on those who have not seen Lost, the cult US drama that began its second series on Channel 4 last week. And even those who can find their way round the island on which Lost's characters can be found have now found themselves lost in another fictional mystery.
Please try to keep up.
A novel connected to the Lost plot was published last week and has already knocked The Da Vinci Code off Amazon's bestseller list. But whereas Dan Brown definitely exists, Gary Troup, author of Bad Twin, does not. Possibly.
The action of Lost springs from a plane that crashes on to a desert island, leaving lots of survivors to tell angst-ridden stories and worry about polar bears.
Now things get more complicated because Gary Troup turns out to be a character in Lost. Actually, not so much a character as a corpse, as he is thought to have died in the plane crash. The survivors discover the manuscript of Bad Twin in the jet's wreckage.
In fiction, the novel remains unpublished. But in real life it is published by Hyperion, a sister company of the makers of Lost, and Amazon is selling it for £10.82.
The US Amazon site cheerfully compounds the muddle with some fiction of its own: "Author Gary Troup delivered the manuscript for his hotly anticipated thriller, Bad Twin, just days before he boarded doomed Oceanic Flight 815."
The publishers are also having fun. A blurb explains that Bad Twin is about a good twin seeking his other half who has to be found so that their dad can divide up the family fortune.
The blurb ends mischievously: "Bad Twin is a suspenseful novel that touches on many powerful themes, including the consequence of vengeance, the power of redemption, and where to turn when all seems lost.
"Bad Twin is a work of fiction and all names, characters and incidents are used fictitiously; the author himself is a fictional character."
One Amazon reviewer asked: "So which world does the story of Bad Twin belong to? Our world or the world of the Island? So now we have a fiction within a fiction, a mystery within a mystery."
Some have suggested that the real author of Bad Twin may be Stephen King. Others, moving on from the suggestion that Lost's island is a place where sinners redeem themselves before entering Heaven, have spotted that "Gary Troup" is an anagram of "purgatory". Which has led to suggestions that new novels may be about to appear by Troy Graup, Pat Urgory and Ray Trugop.
