Insula Sacra (Sacred Island) is a factional novel about an 18th century Limerick surgeon who pioneered methods of treating cataracts, amputation and head injuries. He also inspired the foundation of a College of Surgeons in Dublin. Proud of his Gaelic heritage, Sylvester O'Halloran wrote significant histories of Ireland and contributed to Charlotte Brooke's Reliques of Irish Poetry. His pamphlet Insula Sacra urged the preservation of Irish annals, leading to the setting up of the Royal Irish Academy. As a Catholic, O'Halloran welcomed Grattan's attempts to gain independence for Ireland and to repeal the Penal Laws. Late in life, he supported the resistance to the Act of Union.