Aspiring singer-songwriters set up on nearly every street corner in Cambridge, Massachusetts, and any time of day, it seems, the tubes are alive with the sound of music. International superstars Tracy Chapman, Mary Lou Lord and Martin Sexton all got their starts on those sidewalks and subway platforms around Harvard Square. Milwaukee expatriate Peter Mulvey seems on the brink of joining this elite crowd. One difference, though: After getting good enough to climb out of the tunnels, Mulvey was eager to return.... Read more