Enid Blyton gave us the Famous Five and Fatty's Find-Outers, the Enchanted Wood and the Wishing Chair. Some of us, encouraged by austere critics, have pretended no longer to want what Enid gave. We have pretended that we were not once upon a time ''enthralled'' by her stories. We have chosen to forget how much we loved the time we spent in their company. And we have feigned disdain. Now, Duncan McLaren offers lapsed devotees the possibility of honest redemption. If you're willing to acknowledge that Enid Blyton once mattered to you, you are warmly invited to accompany Duncan on an adventure that will investigate what made Enid Enid and endeavor to reach the source of her torrent of stories, those that came when she was ''letting her mind go free.''