A somewhat dark and scary adventure

I found this one to be a much darker Famous Five adventure than the ones that I have so far read. It seemed that the Five were in a lot more trouble, and facing a lot more danger, than they have had previously. Also, it is the first book that I actually hoped that they would do something to actually kill one of the bad guys (namely by pushing him out of a cave halfway up a cliff) though that was only a fleeting thought because people don't die in any of Blyton's books (that is something that really only happens in adult literature). They also meet an interesting character, Ragamuffin Jo, who starts off bad, but eventually comes good, and once again it is because somebody showed her kindness (in this case it was Dick).
This one has Uncle Quentin and Aunt Fanny disappear to Spain after Quentin returns from America and Julian, Dick, and Anne return from France (why don't they ever have an adventure on the continent?). In this book, like the previous one, they don't find adventure, the adventure finds them, and this adventure arrives in the form of Ragamuffin Jo. Once again somebody is after Quentin's work, and this time they will stop at nothing to get it, which involves kidnapping George and drugging Timothy.
For most of the adventure. George and Timothy are out of the picture. Anne also disappears for a while and Julian, Dick, and Jo leave her and Kirrin Cottage to travel down the coast in an attempt to rescue George. However, the crooks this time are people that you don't mess with. It is very clear from these characters that they will stop at nothing, even murder, to get what they want. However, they did not anticipate the ingenuity of the Five, or that Jo would turn traitor on them simply because Dick showed her kindness.
Once again, Blyton seems to have stepped away from the formula that she had been using in the previous books, in that they don't stumble onto trouble, but rather trouble comes looking for them. Unlike the previous book it is not because they met up with somebody, but rather that the crooks are coming directly at the Five themselves. As I said, this is a much darker, and in a way scarier, story than the others that I have read, though I suspect that Blyton may back away from this darkness in later books (though we shall see once I get to them).