This is a great example of a typical Thorndyke novel. With the eccentric and facetious Penrose speaking in riddles and behaving in the most suspiciously secretive manner, his weird and wonderful collection, his rather lugubrious butler Kickweed, to say nothing of the inimitable Thorndyke and Jervis, we have some fascinating characters to enjoy. The plot is, as usual, intriguing in the scientific complexity of its deductions. Provided you admire the genre, turn of the century, restrained British gentlemanly detective plus sidekick, I think this is a very fine example. If you are a Sara Paretsky addict, leave well alone. If you prefer Sherlock Holmes, this could well be the right choice for you.