In Chapter One of The A.B.C. Murders, Poirot receives a letter. What does it say?

In Chapter One, Poirot receives a letter forewarning of a murder to take place in Andover. Hastings thinks this is the work of madman, but Poirot takes is seriously. The letter is signed by ‘ABC,’ and although Poirot does not care who he is, he does care about why he has decided to write to him and why he would want to do this.