"Secret Alliance" contains in three volumes a detailed study of the Danish Resistance Movement during the Second World War. The study is based upon a comprehensive collection of documents, which survived illegality and were found and made available by the author who, parallel to his search, procured accounts from leading members of the Resistance to fill unavoidable gaps in the contemporary material. The books deal with Danish Resistance in all its aspects, and while describing the gradual development of resistance activity they analyse Denmark's peculiar situation, formally never at war with Germany, but de facto participating in the common Allied struggle and therefore considered by friend and foe as an active partner and opponent. Great emphasis is laid upon the movement's very close connections with the outside world, especially its intimate co-operation with the Western powers, canalised mainly through the British SOE organisation. The books also deal with the political structure of the movement, its relations to the official political circles, and its efforts to bring an official policy of negotiation with the occupying power to its downfall - an attitude which in 1944 led to the recognition from the Soviet Union of 'Fighting Denmark', the movement thereby paving the way to a formal recognition of Denmark as an Ally.