The haunted mind of a brave patriot; a bitter betrayal by the Third Reich, soothed by the arms of a forbidden affair.

On Either Side is essentially a love story set during World War II between a young German SS Officer, Karl Wulf, and an English nurse Brenda King. The couple meet late in the book when Karl is wounded at the Battle for Caen and brought to a British Field Hospital on the outskirts of the city.

Before this Karl is awarded the Knight's Cross for courage and loyalty to the Reich demonstrated on the Eastern Front, and is assigned by Heinrich Himmler for rest and recuperation to the Sobibor death camp in a benign role to convalesce for a few weeks before being sent back to active service. Here he discovers the true purpose of the camp and is appalled and mentally scarred by the genocide he witnesses. With the help of another guard at the camp he plans a successful escape of a small group of Jewish prisoners.

However, he is suspected of collusion with the escape and so sent back to Berlin. But Himmler admires the qualities of Karl, his bravery and conscientiousness, and adopts him briefly as a confidante before being reunited with his Sobibor co-conspirator and being sent to Limoges in Vichy France to take over command of an SS field base at Masset Farm in Oradour-sur-Glane (village infamous for the Oradour massacre).

With the onset of the D-Day invasion, Karl's orders are changed and he is sent to Paris, under the supervision of the German hierarchy, to root out Jews hiding in the city for deportation to the death camps. But his conscience couldn't entertain such orders and so, before he leaves for Paris, he arranges an escape route, with the help of a local priest, for Jews from Paris to a temporary safe house at Oradour en route to freedom in Spain.