We know from references in other books in the series that the events of 'Peter Duck' didn't happen within the fictional lives of Ransome's heroes; rather, it's a metafiction - a narrative that they composed together in the cabin of an old wherry over the course of a winter holiday. There's no such intertextual reference to Missee Lee in the canonical stories, but nevertheless we know it is a sequel to Peter Duck. We know this because we find our heroes on the same little schooner that Peter Duck had helped them sail before.
So we know from the start that Missee Lee is also a metafiction, or rather, a metafantasy: a fantasy of a China which never existed but which, one cannot help thinking, should have.
Missee Lee is the most sustained comedy in Ransome's oeuvre. The first chapter gives us none of this: it's a rattling good yarn in the best tradition of rattling good yarns. But as soon as our heroes get ashore and meet the eponymous pirate queen, a twist no-one would have predicted takes the plot by the tail. Roger is discovered to have just one unique talent - a talent which none of the others had ever thought might come in useful; and throughout the delightful romp which follows, this unlikely talent is the one thing which saves everyone's life.
In summary, this isn't a 'Swallows and Amazons' tale like any other. It stands alone. It's more exotic, funnier, odder, and ultimately more poignant. But it is probably some of Ransome's finest story telling, and certainly his finest writing. And although aimed at a teen audience, this really is a story to delight any reader.
Read it, as they say, and weep - but weep from laughing.