In the title mol-ecule, C21H20ClN3OS, the tetra-cyclic system is close to planar [r.m.s. deviation = 0.110 (4) Å]. The dihedral angle between the quinoline ring system and the benzene ring is 178.3 (1)° and the angle between two (S-C=C-N) halves of the thia-zine ring is 173.4 (1)°. In the crystal, mol-ecules are arranged via π-π inter-actions [centroid-centroid distances = 3.603 (2)-3.739 (2) Å] into slipped stacks extending along [010]. Inter-molecular N-H⋯O hydrogen bonds link the amide groups of neighbouring mol-ecules along the stack, generating a C(4) motif. The title compound shows promising anti-proliferative and anti-cancer activity.