A maker of history (E. Phillips Oppenheim)

In this romantic story tells about how in 1905 a young British tourist accidentally witnesses a strange meeting in Germany. Then, in Paris, he tells about it not in the company where it could be shared. His sister, who had to meet with him finds his brother’s baggage at the hotel, but he himself disappeared. The French police are pretending to be looking for him persistently, but then the sister himself disappears. A childhood friend who is in love with her is asking her friend to help in the search. He agrees to look for this pair, finds hints, but gets a warning to stop the search.