Casey was one of a group of Fenians arrested in 1865 in Cork and transported to Western Australia with other Fenians captured in the abortive 1867 Rising. "A Mingling of Swans" includes Casey's unpublished account of his experiences as a convict on roadwork parties, as well as correspondence by Casey and other Fenians, and some articles by Casey on his impressions of Western Australia which were published in Dublin separatist newspapers. Casey portrays with humour and determination the harsh conditions endured by Fenian prisoners.