Complex sentence: The book follows Henry Perowne, a middle-aged, successful surgeon, five chapters chart his day and thoughts on Saturday the 15 February 2003, the day of the demonstration against the 2003 invasion of Iraq; the largest in British history.
Split into simpler sentences: The book follows Henry Perowne, a middle-aged, successful surgeon. Five chapters chart his day and thoughts on Saturday the 15 February 2003, the day of the demonstration against the 2003 invasion of Iraq, the largest in British history.