Murder in Montparnasse by Kerry Greenwood

Seven Australian soldiers, carousing in Paris in 1918, unknowingly witness a murder and their presence has devastating consequences. Ten years later, two are dead ... under very suspicious circumstances. Phryne's wharfie mates, Bert and Cec, appeal to her for help. They were part of this group of soldiers in 1918 and they fear for their lives and for those of the other three men. It's only as Phryne delves into the investigation that she, too, remembers being in Montparnasse on that very same day.