The central premise is 'what if Sherlock Holmes was an eleven year old girl?,' but in truth Sherlock and Friday don't have much in common apart from a lack of social skills and a gift for solving mysteries (on the other hand, what more do you need?) Here I must confess that a few years ago, I was toying with the idea of a pair of eleven year old girls as Sherlock and Watson -- it must have been when I first came across BBC Sherlock. My sleuths were called Charlotte and Joss... and that's about as far as I got before I realised that while Sherlock and his imitators have a gift for solving mysteries, I sadly lack the gift for creating them. But RA Spratt has succeeded splendidly where I failed to even cross the starting-line.
At first I found Friday's world oddly hard to place -- was she living in America, the UK? The cultural markers were weirdly elusive, deliberately so, I suspect, as the series has sold into the US. It was a relief to discover that RA Spratt actually lives in Bowral. But it was slightly weird to read a world (mostly boarding school) which is sort of Australian, but not really -- a kind of fairly white bread, Australian-ish alternative universe. (To take a trivial example, TimTams are clearly described, but not named as such -- because poor USians don't have them over there.)
But overall, Friday Barnes is a lot of fun to read, and, I suspect, lots of fun to write, too.