First off, every place I checked (not only Goodreads) lists "Zadok's Treasure" as number 2 in the series and "The Cape Cod Caper" as number 3. This is wrong. I started out reading "Zadok's Treasure", growing suspicious as Penny and Toby continually referred to two previous cases, one having taken place in Cape Cod. At about page 25, 26, a name was mentioned as discovering a body in a bog during the last case. A quick check revealed the name and circumstance happening in "The Cape Cod Caper". Thus, every list has books 2 and 3 listed incorrectly, so if you're reading the series in order, be forewarned and read "The Cape Cod Caper" before "Zadok's Treasure".
On to the story. "The Cape Cod Caper" was much better than the first book. The pace didn't plod like the initial entry into the series and the story was more engaging. At first I feared Toby wouldn't feature much, if at all, in this book, but I liked the way Margot Arnold involved him in the case. The only drawback was that too many conclusions are easily guessed by the reader (this reader, at any rate). I wasn't sure if I'd continue with the series after the first book, but already having a copy of "The Cape Cod Caper", I purchased what I thought was book 2 and pressed on. Now I'm glad to have "Zadok's Treasure" awaiting and plan on giving this series at least one more read.