The German invasion of Poland began on 1 September 1939. On the advice – seriously flawed, as it turned out – of British general, Sir Adrian Carton de Wiart, resident in Poland, on 5 September, the family fled East. They went to stay in Mołodów, Polesie Voivodeship on the estate of Henryk Skirmunt and his sister, Maria, the younger siblings of Konstanty Skirmunt, Polish ambassador in London (1919–1934). The plan had been to overwinter there and that Ciechanowiecki should attend school in nearby Pinsk. On 17 September invading Soviet units laid siege to the small town. Elements of local Belarusian activists presented an ultimatum to the Skirmunts: that the 150 Polish military police stationed on their estate should lay down their arms or all the buildings would be set alight. The unworldly Skirmunts fell for the trap; the police were all shot with their own weapons, the elderly Skirmunts were slaughtered in the woods and all the premises looted. Ciechanowiecki and his family managed to flee the horror with the retreating Polish columns of general Franciszek Kleeberg. Ciechanowiecki later stated laconically: "...coś tam pomagałem, mam nawet krzyż za kampanię wrześniową jako ochotnik." – "I helped out a bit, I even have a cross for the September campaign, as a volunteer." They travelled via Kamien Koszyrski to Kowel, then by train, strafed by Soviet planes, on to Lwów. There they suffered a harsh winter and a failed attempt in December to cross the "Green frontier" into Romania. They left the city in March 1940, just two days ahead of the KGB's arrival to start mass deportations. Recrossing the new "frontier", they finally returned to Warsaw in early May 1940.