The series is written by Helen Moss and published by Orion Children's. There are currently ten books in the series, but in a recent blog post, Helen Moss said that at least another four are planned.
The series is set on the invented Castle Key Island, which lies off the Cornish coast. This great map is typical of the lovely line illustrations by Leo Hartas which accompany the stories. As this is a nice safe island (despite the relatively high crime rate!), where everyone knows everyone else, the children can be free to roam around and investigate.
The characters are a key strength of the series. My daughter and I are particular fans of Emily Wild, who lives on Castle Key with her parents and her lovely dog, Drift. The other investigators are Scott and Jack Carter, who spend school holidays on Castle Key with their Aunt Kate, a romantic novelist. Emily is really the leader of the group, making plans and gathering clues in her notebook. One of the great things about reading a really good series is the familiarity you get with the characters, and I saw that this week in reading book 10, The Invisible Spy, with my daughter, when Emily underlined the case's title in her notebook (twice, I believe). We both smiled, because that sense of organising ideas and being neat is absolutely typical of Emily.
Drift is great too, and I particularly like that occasionally the narration will shift to his point of view.
"Drift shot out from the sofa. Distraction was his all-time favourite command. He just had to find something really naughty and do it! And this time he knew exactly what his Naughty Thing was going to be!"The point of view shifts occasionally between the characters, which helps strengthen the characterisation and is always clearly signalled like the example above.
The plots are involving and intriguing. The mysteries are real and effectively planned, with red herrings and twists to keep you guessing, while not being confusing for the child audience. In the last few stories there have been smugglers, scientists and secret agents, not to mention dinosaurs, rock concerts and wreck diving. I strongly recommend these for 8+ - and that absolutely includes adults. I love these books!