The title refers to the The McGuire Sisters, a hugely popular 1950's and 1960's singing group comprised of 3 sisters singing in perfect three-part harmony. Among their most popular songs were "Sincerely" and "Sugartime", both million-selling number-one hits. The McGuire Sisters became one of the biggest acts in Las Vegas, Atlantic City and New York City night clubs during two decades and performed for five U.S. Presidents and Queen Elizabeth in London. They retired from public appearances in 1968, giving their last performance that year on The Ed Sullivan Show. They were inducted into the National Broadcasting Hall of Fame in 1994, the Vocal Group Hall of Fame, and numerous other Halls of Fame and the Hollywood Walk of Fame.