Care should always be taken to avoid what Fowler calls the "false scent" that comes from grouping words in a way that suggests a different construction from the one intended, however fleeting the suggestion may be. In the sentence:
'Behind each part of the story I shall tell lies an untold and often unsuspected story of hard work...."
the words "I shall tell lies" irresistibly group themselves together until the eye has passed on. Never try to correct this sort of thing with a comma; always reconstruct.