The title compound, C17H10S4, has two independent molecules in the asymmetric unit. In both molecules, the fused heterocycle is almost planar and the phenyl groups make dihedral angles of 42.88 (9) and 52.79 (8)degrees with the fused heterocycle in one molecule, and angles of 40.62 (9) and 52.28 (8)degrees in the other. The crystal packing is governed by short intermolecular S . . .S interactions, the shortest contact being 3.333 (1) Angstrom.