Is there any torture as sharp, any prison as confining, any punishment as cruel, as regret? For, although Prisoner 5863 is locked down in “extreme isolation,” he really isn’t isolated enough. Regrets small and large crowd his mind as he sorts through the decisions that cost him his name and his freedom. In 5863, a powerful solo piece written and performed by Rudi Stroebel, one man struggles to puzzle together pieces of a shattered life. Whether he can find some wholeness and peace in the darkness of his cell (and his mind) is the driving question behind this remarkable, enthralling new work. Angela Grillo and Dominique Sire direct at Eclectic Company Theatre.