What is the main conflict in Pegasus Bridge: June 6, 1944 by Stephen E. Ambrose?

Pegasus Bridge by Stephen E. Ambrose is the fascinating story of the role of British Company D in the Allied invasion of France. Company D was a small detachment of one 181 men under the command of Major John Howard. Their assignment was to secure the bridges over the Orne River and the Caen canal and to hold them until they were relieved by the beach landing forces.