It is little known today that, in January 1939, the IRA launched a bombing campaign, codenamed The S - or Sabotage - Plan on mainland England. With cynical self-justification, they announced that it was not their intention to harm human life but in just over a year, more than 300 explosive devices resulted in 10 deaths, 96 injuries and widespread devastation. London, Birmingham, Manchester, Liverpool and many other towns and cities were targeted. On 25 August 1939, detectives in London defused three devices set to detonate that afternoon at 2.30 and arrested four terrorists. At the same time an identical bomb exploded in Coventry city centre killing five civilians and injuring 50, the highest body count of the campaign. Numerous arrests were made nationwide but ill-trained personnel and additional national security resulting from the threat of Nazi invasion caused the campaign to falter and fade away in early 1940. The author, a former detective, is well qualified to write this book, having spent 18 months in Northern Ireland combatting terrorism, for which he was commended by the Metropolitan Police Commissioner, Lord Imbert, for displaying ‘courage, dedication and detective ability’.