R. Austin Freemans mysteries are often divided into two parts, the first dealing with events leading up to a murder, followed by Dr.
In this case, the first part, about a beautiful woman who poses as a serious artist, then disappears, is delightful. The second part is written in the first person with Jervis, Thorndykes assistant, being the narrator as usual.
But thanks to an unseen witness, the killer may be caught, and the witness turns out to be a blessing in disguise.