forum. in 1970, sondheim began a collaboration with theater pro pro producer hal prince that lasted more than a decade. their 1973 play, a little night music, was composed mostly in waltz time and became one of their biggest commercial successes. it featured the hit send in the clowns. one uof sondheim s best-known songs. in 1979, sondheim wrote what was probably broadway s first musical thriller sweeney todd. the story of an english barber and serial killer. what s great about the theater is it s a living organism, whereas movies and television are as if in amber. it s not that they re dead but they re only alive in one shape,