The Secret Adversary by Agatha Christie (Pan, 1958 and 1963)

Here we have two versions of the same book, from the same publisher, but printed five years apart.  They provide proof that while things always change they don't necessarily improve.   First, the version from 1958:

 

THE SECRET ADVERSARY tells how two young people advertise for adventure and are caught in a whirlpool of international intrigue which almost costs them their lives.  A gay and exciting thriller!

 A woman, held at gunpoint, hands over documents to the mysterious figure in the foreground.  The cover doesn't tell you who the woman is, or what the documents are, but it certainly lets you know that what you're about to read is a crime thriller.

Next, the version published in 1963:

Two Innocents in search of adventure.

An Elusive Young Woman holder of a vital secret

A Faceless Man with a Blueprint for Anarchy

The woman being held at gunpoint has been replaced by a picture of a dark and gloomy mansion.  While the art isn't bad, the contents of the book could be anything: a Gothic romance, a collection of ghost stories, and traditional murder-in-a-country-house whodunnit.

At least Pan's copy writers had learned to write snappier blurbs for their back covers--albeit ones with really strange ways of using capital letters!