The M tro Murder is one of the most famous unsolved crimes of the 1930s. Who was Laetitia Toureaux? What were her links within the murky world of spies and secret political movements? All of those things remain shrouded in mystery, despite the fact that her movements on her final day are well documented. How was she stabbed to death in an apparently empty M tro carriage? And by whom? A Small Thing for Yolanda offers one potential solution.