The title compound, C26H26N2·0.5C8H10, is the first reported characterized 2:2 product from acid-catalyzed condensation of indole with cyclopentanone and no other 2:2 products were observed. Recrystallization from p-xylene gave the title hemisolvate with the p-xylene molecule located about an inversion center. The terminal pentalene ring is envelope-flap disordered at the C atom farthest from the skeletal indole unit, with a refined occupancy ratio of 0.819 (4):0.181 (4). The major component has this C atom bent away from the spiro-fused cyclopentane ring. In the crystal, molecules are connected by N—H...π interactions, forming chains along [100], and N—H...π and C—H...π interactions, forming chains along [001], which results in the formation of slabs parallel to (010).