Monday’s TV Highlights: ‘Supergirl’ on CBS

SERIES

Supergirl Laura Vandervoort —who played Supergirl in the series “Smallville” — guest stars as Indigo, an enemy who commits her evildoing by traveling through the Internet. Melissa Benoist stars in this new episode. 8 p.m. CBS

The Voice The singing competition returns for a new season. 8…