I used to surmise that Ms. Hussey is the felon; there is a decisive change at the moment. The anecdote has changed my way of understanding by leaps and bounds! Presently I am realizing that the miscreant is someone else... So far I have read that Petra and Calder have started to realize and worry that Ms. Hussey is verily involved in this theft, after she is giving away clues and has raged a discussion in class. No sooner the children start to experience strange coincidences and manage to grasp more clues with the help of a Charles Fort book titled Lo ! Situations, when the LADY starts to appear in Petra's dream were like a bolt from the blue! Later on, Calder encounters sundry happenstances while completing his assignment to find an artistic object as told by Ms. Hussey. Suddenly, the story moves on to narrate Frog's - Tommy's new neighbors in New York, sudden disappearance and Tommy's mother's new husband, Old Fred.
Later on, they both find themselves quiet familiar with Vermeer and his paintings after they happen to meet Mrs. Sharpe and I feel that she might be the anonymous to send letters and steal the lady. Keeping that aside, both the children have already started to learn more about Vermeer and have had several coincidences because of the book Lo! And Calder's pentominoes of course! Also, because the anonymous is sending public letters and publishing advertisements in the newspapers; the whole place has started to admire and look up to art and other details more closely. Many protests and rallies were also depicted in this book so as to protect the lady and to identify REAL works of Vermeer as stated in the story.
This narrative has so far been full of twists and turns. I was definitely wrong about the actual culprit, as the story has many more characters to go through! Presently, this book has focused more on obscure coincidences and may continue to do so till the mystery unfolds.