Tresckow, however, had a backup plan. During the lunch in question, he asked Lieutenant Colonel Heinz Brandt, who was travelling with Hitler, whether he would be good enough to take a bottle of Cointreau to Colonel Helmuth Stieff (who was not yet a conspirator at that time) at Hitler's headquarters in East Prussia as a payment for a lost bet. Brandt readily agreed. The "Cointreau" was actually a bomb constructed of a British plastic explosive "Plastic C" placed into the casing of a British magnetic mine, with a timer consisting of a spring which would be gradually dissolved by acid. Before Hitler's Condor plane was to take off, Schlabrendorff activated the 30-minute fuse and handed the package to Brandt, who boarded Hitler's plane. After takeoff, a message was sent to the other Berlin conspirators by code that Operation Flash was under way, which they expected to take place around Minsk. Yet when Hitler landed safely at his East Prussian headquarters, it became obvious that the bomb had failed to detonate (the extremely low temperatures in the unheated luggage compartment probably prevented the fuse from working). The message of failure was quickly sent out and Schlabrendorff retrieved the package to prevent discovery of the plot.