The Casque's Lark; or, Victoria, The Mother Of The Camps: A Tale Of The Frankish Invasion Of Gaul is the fifth book of Eugene Sue's 21 volume series The Mysteries of the People; or History of a Proletarian Family Across the Age. The series was created to be a European history that depicts the struggle between the ruling and the ruled classes. One family, the descendants of a Gallic chief named Joel, represent the oppressed and the descendants of a Frankish chief Neroweg, typifies the oppressors. Down through the ages the successive struggles between oppressors and oppressed are depicted in a series of stories that culminate in the European Revolutions of 1848. The first four titles in the series served as an introduction to the Gallic people and tells of their situation in Europe from Julius Ceasar's conquest of Gaul to the death of Jesus.

In this volume, set in the third century AD, we first meet Frankish invader Neroweg as he tries to cross the Rhine River to conquer the Gauls, steal their land and rape their women. He is opposed in this effort by Victoria, the wife and daughter of great generals, and her son Victorin, the newly elected leader of the troops. Joel's family is represented by Schanvock, the adopted brother of Victoria who aids Victorin in battle. While Victorin battles Neroweg, Victoria faces a much more insidious threat from her cousin Tetrik, a Governor of a Gallic province, whose ambitions threaten Gaul from within.

As the Roman Empire fades and its hold on Gaul loosens, the threat on the people and the land now come from the Frankish tribes of the north and alliances between Tetrik and the new Christian bishops of Rome.

The lark of this story is the insignia of a Roman troop defeated by a Gallic force. They portrayed their victory by displaying on their shields a Gallic Rooster holding the Roman lark in its talons. This symbol was cast in bronze as a crest on Victoria's war helmet, or casque.