They were one of the iconic pairs in country music and the most popular duo of their time, selling millions of records between 1967-1976 and yet Dolly Parton's seven-year, star-making run with Porter Wagoner is often relegated to the opening act in Dolly's story -- the dues she paid before she turned into an international superstar and a legend. Hits compilations appeared like clockwork over the ensuing decades but Bear Family's 2014 six-disc box Just Between You and Me is the first real reckoning with that legacy, offering it in its entirety along with a hardcover book by Alanna Nash that tells the tale. When Wagoner hired Parton he was searching for a replacement for Norma Jean, the singer who was his duet partner for the first half of the '60s and an important component of his stage and television shows. Jeannie Seely already had come and gone and Porter was in need of somebody stable yet tough enough to provide a credible counterpoint to his flinty country corn. Enter Dolly Parton. She had just released her first record and was in need of exposure, so they both met each other's commercial needs but, happily, they turned out to have potent natural chemistry. Unlike such contemporary pairs as George Jones & Tammy Wynette or Conway Twitty & Loretta Lynn, Porter & Dolly lacked any inkling of romantic melodrama. They'd sing songs of love or cheating but it never seemed more than an act, a persona they'd adopt for the stage, which was part of their brilliance: Porter & Dolly shared a love of kitsch, realizing that beneath the pantomime there lay an emotional truth. This gave the greatest of their hit singles -- "The Last Thing on My Mind," "Holding on to Nothin'," "Just Someone I Used to Know," "Please Don't Stop Loving Me" -- a resonance, but the facility with showbiz meant they could sing any old thing and charm. Certainly, they sang their fair share of novelties and schlock, as this box makes abundantly clear, but they grounded the flights of fancy with their dose of "sugar and vinegar." At their best, which accounts for much of the music they made between 1967 and 1972, they seemed as equals and yet a close listen reveals how at the beginning Wagoner had a slight upper hand while Parton dominates during the twilight. This subtle shift gives the music itself a narrative arc -- there was a mess behind the scenes, involving lawsuits and bitter spirits, all which Nash details -- but this always absorbing box proves in all the ups and downs and everything in between there never was another duo like Porter Wagoner & Dolly Parton, nor is it likely there ever will be.