Rin-Tin-Tin, Lassie, The Littlest Hobo, Digby - the Biggest Dog in the Word: all of them were smart mutts (except, perhaps, the last one) but they're all as naught compared to Olaf Stapledon's shining and eponymous Sirius; a dog every bit as clever as the humans who created him.

Sirius gets underway remarkably quickly; the scientific elements are entirely secondary to the anthropological. Thomas Trelone is a brilliant scientist who has discovered a way to increase the intelligence of the higher mammals and the star of his programme is Sirius, a huge Alsatian crossbreed with a brain far larger than the rest of his species.

From early on it becomes apparent that this canine Einstein will follow a lonely orbit. Other dogs, even the less successful 'super dogs' of Trelone's continued experiments, are no better than morons compared to Sirius' enhanced perception, but at the same time the humans he can call his equals are (no matter how benignly) the rulers of his world. And it is a world set up for bipedal, dextrous, tool using apes, not four-legged and clumsy dogs.

Sirius is raised within the loving and nurturing circle of Thomas's family; his own (oddly named) daughter Plaxy becomes the dog's inseparable childhood companion and it is this that causes Sirius to first become aware of his unique nature, when Plaxy is sent off to school whilst Sirius must take some "work experience" as a local sheep dog.

Their diverging experiences of life and their recognition of their great differences drive Sirius and Plaxy apart in manner faintly reminiscent of Heathcliff and Cathy in Wuthering Heights, only to bring them resoundingly back together later on when each realises what a powerful and unique relationship they have.

There are, inevitably, rather more echoes of Frankenstein throughout Sirius, but there are no direct allusions to the earlier novel that I was aware of; rather these two books deal with convergent themes, that of the permanent outsider in human society who can never truly fit in but can only be fleetingly accepted - by Sirius' first sheep-farmer master, by Trelone's scientific colleagues at Cambridge and by a family cousin in London's East End, a vicar.

In keeping with Stapledon's disinterest in Science (perhaps this is too strong, but Stapledon is not so interested in Science per se as in the meaning(s) we can draw from its revelations), the Cambridge scholars are the least interesting of those whom Sirius encounters. It is the man of God and the man of Nature who are the more accepting and more intriguing.

But ultimately Plaxy means the most to Sirius, and vice versa, and it is her love that redeems Sirius throughout the book. It also allows for a great section, which had me laughing out loud, where Sirius surreptitiously manages to send Plaxy a letter.

Stapledon's prose manages to project Sirius's alien-ness throughout the book without ever losing sight of his…I want to say 'humanity', but it's less oxymoronic to say his commonality with man. Without using any modernist or postmodernist tricks, Sirius presents a very straightforward narrative that takes up where Frankenstein left off, but has a 'monster' largely unhampered by a hideous exterior but who is, in the end, still defeated by a humanity ill at ease with what it doesn't understand.

Sirius is only a short book; it could easily have been far longer and perhaps more insightful, but I think Stapledon was right to restrain himself so that Sirius is a parable where it could have been an inquiry, and consequently it retains a greater emotional resonance than either Star Maker or Last And First Men.

Marvellous stuff from a writer still sorely undervalued.