Blutch who has deserted and who tries to sow Sergeant Chesterfield falls on a dying Northern soldier who just has time to reveal to him a terrible secret before he dies: President Grant will be murdered by one of his army members. Returning to the camp, Blutch warns the president who eventually believes him after having escaped a first attack. Chesterfield becomes the close guard of President Grant, while Blutch is sent by General Alexander, under the command of Captain Stark, to conduct a small investigation into the neighbouring Southern village. Everything will lighten up when Stark returns to Abigail, the sister of Captain Stilman.