Each generation rewrites (or in the case of film, re-shoots) past history according to its own value systems. So it is not surprising that Rosemary Sutcliff’s posthumous Sword Song, written five years ago when she was in her seventies, already seems old-fashioned.

Too often her ancient Norse sailors and farmers come over like idealised 1930s school prefects, firm in their judgments, quick to grin or give a slap on the back, and strikingly uninterested in the opposite sex. Oaths are kept and promises remembered. The respect for a chivalric code of service held by the powerful and the powerless takes the sting out of any description of the exploitation of one character by another.

The detailed set pieces are, as always, impressively well-informed. But the voice of the schoolteacher is never far away, insisting on points of authenticity to the extent of using hosts of unfamiliar words. One page alone contains “greasy wadmal”, “war-sark” and “sea-kist”. With a roll-call of characters that includes Erp, Groa, Orm, Gisli and Aud, the story may cause young readers to laugh at rather than with a story whose moments of humour are few indeed.

Sutcliff herself would not have understood the reasons for any giggling, coming as she did from a tradition that honoured the past as part of the universal respect expected of the young for the old. But a different spirit rules today, more of Monty Python than Rudyard Kipling. Some paperback history books written for children strain for a laugh as never before, even - or sometimes especially - when describing human cruelty.

Sutcliff always showed a more compassionate attitude, knowing pain at first hand from her own childhood experience of arthritis and the agonising treatment she was put through. But serious history does not have to mean a heavy read, and there are moments when Sword Song starts to drag. Sutcliff was only halfway through the second of her usual three drafts when she died in 1992, which could explain some of Sword Song’s more repetitive passages.

It tells the story of Bjarni, an exiled youth who spends five years working as a hired blade in Scotland and Ireland. But apart from a vivid description of witch persecution, there is little of the otherness of different times and people here. The infantile rages, obsession with rank, crippling superstitions and unstable emotions of ancient history find small place in the hearty, sexless and ultimately rational world Sutcliff describes.

The overall picture she paints is generous with incidental detail but lacks conviction at a personal level. Young readers who know nothing of the past may guess, simply from the evidence of their own lives, that humans have always been more unpredictable than they appear in these pages.

Sword Song is therefore only a partially successful swan song from an endearing and courageous author, who in her latter years sometimes promised more than she was ultimately able to deliver.