It originated in a 1953 novella, but the full-length version wasn't published till 1961. Where The Broken Sword is a full-blooded saga-style tale, Three Hearts and Three Lions is a modern-hero-whisked-away-to-fantasy-world story, with a lot more humour (though it isn't a comic novel) and more than a touch of the moonlighting SF writer on show.
Holger Carlsen is a young Danish man with a mysterious background, whose secrets both he and the reader discover as the book proceeds. We first meet him in the US just before the Second World War, through the eyes of a nominal narrator who simply relates the tale Holger later tells him in third person. Holger ends up fighting for the Danish Resistance against the Nazis and, in the middle of a crucial fight, finds himself whisked away to a world loosely based on the Carolingian legends, complete with dragons, trolls and the Kingdom of Faerie.
At first, all Holger wants is to get home, but he seems in some way to belong in this world. He links up with various companions: the dwarf Hugi, the swan-maiden Alianora and, later, the Saracen knight Carahue — not to mention the feisty steed Papillon who seems to be his — and finds himself caught up in a great war between Law and Chaos to decide the fate of the world.
As a science fiction writer, Anderson was very much part of John W. Campbell's stable and, although he was too late to publish in Campbell's fantasy magazine Unknown Worlds, Three Hearts and Three Lions is very much in its tradition. It's slightly reminiscent of Pratt & de Camp's Harold Shea stories in its analysis of the world of legend the hero finds himself in, though less outright comic.
Holger is an engineer and scientist, and he can't help trying both to explain what's happened to him, using theories of alternative universes, and to find scientific explanation for issues like how magic works and why the fae can't touch iron. In a memorable scene, he defeats a dragon by tossing several helmets-full of water down its throat. He explains to his astounded companions:
Look, if the creature breathed fire, then it had to be even hotter inside. So I tossed half a gallon of water down its gullet. Caused a small boiler explosion.
For the first few chapters, as Holger wanders around gathering companions, the story threatens to topple over into aimlessness, although all the characters are engaging enough to maintain interest. Long before this becomes a problem, though, the pace and sense of purpose pick up, and the story builds to an exciting climax.
It's not perfect. The narrative cuts off somewhat abruptly, jumping forward to Holger meeting the unnamed narrator again after the War, and showing us nothing of the great battles we've been building up to. In a way, I can understand that — the story's really about getting him to the point where he can be the Champion of Law — but it seems incomplete without some idea of what happened next.
I also found the faux Scots dialect of both Hugi and Alianora a little annoying. It didn't distract me too much, and both are too good as characters to put me right off, but it wasn't very convincing.
One other criticism is no reflection at all on Anderson and the novel, but I couldn't resist mentioning the cover of the 1974 Sphere edition (reproduced above). The illustration shows an implausibly half-armoured, half-naked warrior on a light-coloured horse and carrying a red shield, smiting a dragon with his sword. In fact, Holger wears complete and sensible armour, which Anderson carefully describes, rides a black horse and carries a predominantly blue shield. And, while he faces a dragon, we've seen above how he actually deals with it. One more example of a cover artist neither reading the book nor being properly briefed.
Nevertheless, carps aside, Three Hearts and Three Lions is a wonderful book: exciting, funny, intriguing, romantic and clever. The characters are engaging, from Holger himself and his companions to the villains, including Morgan le Fay from the Arthurian legends, to some delightful bit-parts. The prose varies between completely serviceable and lyrical, and the story serves as a good introduction to the Carolingian legends. I must admit, I only know about these in a very general way, having concentrated more on the Matter of Britain than the Matter of France. I certainly feel motivated to read more now.
It's also a surprisingly important novel. The concept of Law and Chaos, very familiar now, seems to have originated here, although it was subsequently developed by Michael Moorcock (an Anderson fan) in his Eternal Champion cycle. It's been claimed that the original version of D&D took not only its alignments from Three Hearts and Three Lions but also elements of its trolls and its Paladin class.
It's a short novel by modern standards — a mere 156 pages in the edition I have — so there's really no excuse for not reading it. I'd include Three Hearts and Three Lions as one of the classics that any lover of the fantasy genre would do well to read.