The show is set during the Irish Rebellion of the 19th century. British policy was to banish (many were allowed to immigrate to America) or send them to the penal colonies in Australia. A group of Fenians (a precursor to the IRA) were sent to one of these colonies and with the help of their society and an American captain, they plotted an escape. The 'Catalpa Incident' became a worldwide sensation and this daring (and a bit crazy) attempt is discussed in great detail in the show.
As I said, the show isn't bad--it just doesn't really explore history using the dead as a starting block like most other episodes. The show just as easily could have been from an entirely different series.