“Sweeney Todd: The Demon Barber of Fleet Street,” from 1979, may be Stephen Sondheim’s masterpiece: a Grand Guignol thriller about a barber who slits his customers’ throats and his merry accomplice, Mrs. Lovett, who bakes their remains into pies. In 2014, Tooting Arts Club staged its immersive version at Harrington’s, one of London’s oldest pie-and-mash shops. The production opens at the Barrow Street Theatre this week, complete with pie, mash, and its stars, Jeremy Secomb (above) and Siobhán McCarthy.
