Santa Clara CA: Diakonia Press, 1975. Paperback. 142p., text reproduced from double-spaced typescript, first edition plain printed blue wraps, 8.5x5.5 inches. A very good copy.
Grassi does not mean "Christians who lived in caves or in hiding, or groups that held secret meetings to escape the supervision of an 'institutional church' of the time," but the non-canonical, "whose views and life-styles were a striking contrast to much that we find in the canonical," which views were not recorded (merely suggested) in the surviving literature.