A night of unprotected sex leads to a life sentence of single-mom struggles in a mildly amusing indie that's neither as funny nor as poignant as it wants to be. Krysten Ritter, the likably quirky raven-haired star of ABC's new series Don't Trust the B---- in Apartment 23, gives this cliché comedy some fizz, juggling an infant and a dead-end job walking dogs, all while envying her roommates' (Kate Bosworth and thankless third wheel Rachel Bilson) carefree lives. It's a trifle, but at least it doesn't star Katherine Heigl. B-

