Learning to Swim. I wouldn't call it a sequel, because you don't have to read the first book to understand the second book. Though I liked the first book, so recommend you read it first all the same. I haven't read many Agatha Christie, I haven't read any James Patterson books, but I imagine this is what those books are like. The mystery solver is the same through out the books, and you learn personal information about the main character, but it isn't mandatory to know the history to enjoy the mystery.
I like the story again in this book. The main character is again one I enjoy. And I liked the supporting characters in this book. And I liked the whole whodunit at the end (the resolution of the mystery.)