The B Minor Mass is one of Bach’s greatest curiosities. A true piece of musical patchwork, this extraordinary amalgamation of arrangements, recomposed fragments and new ideas together spans more than 25 years of Bach’s career. And yet, Bach never heard it performed. Nor did he expect to – since it fits neither the Catholic or Protestant liturgy, its purpose remains tantalisingly elusive. But in its scale, ambition and dramatic, inexorable unfolding, the B Minor Mass remains one of his most monumental works, a remarkable testament from Bach’s final years.