Aconitine

Aconitine is a chemical alkaloid extracted from the monkshood plant, also known as the devil's helmet or wolf's bane. Symptoms include vomiting, diarrhoea, respiratory failure and cardiac arrest.

Characters poisoned with aconitine

 * 4.50 from Paddington - Harold Crackenthorpe took a pill from a box of what looked like sleeping tablets but which contained aconitine.
 * They do it with Mirrors - a box of kirsch flavoured chocolates was laced with aconitine.