In 1974, the novel "Spy Story" was published, followed in 1976 by "Twinkle, Twinkle, Little Spy" (also known as "Catch A Falling Spy" in North America). As the protagonist also remains anonymous in both of these novels, it is open to debate whether or not 'Harry Palmer' is the same narrator of these last two novels as in the earlier books. There is conflicting evidence for either view. Despite this, and despite the lead protagonist being unnamed, all six books have been unofficially called the Harry Palmer novels, based on the protagonist's name given in the subsequent film adaptations of "The IPCRESS File" and its sequels.