I would like to thank fellow crime writers Brian Innes and Michael Jecks for information on forensic chemistry, document examination and weapons; Judge John Prosser QC for some advice on legal history; Dr Wayne Jones of Linköping University, Sweden, and Professor Derrick Pounder of Dundee University for historical data on toxicological analysis – and Peter Haig and Jeremy Wills of Molyslip Atlantic Ltd for information on lubrication additives. Any errors are due to my misinterpretation of their kind assistance.