Classifying endotrivial kG-modules, i.e., elements of the Picard group stable module category for an arbitrary finite G, has been a long-running quest. By deep work Dade, Alperin, Carlson, Thevenaz, and others, it reduced to understanding subgroup consisting modular representations that split as trivial k direct sum projective when restricted Sylow p-subgroup. In this paper we identify first co...