“Janet Planet” is a phenomenal debut by Annie Baker, a MacArthur genius grant-winning playwright who has notched so many theater prizes that she may have grabbed a camera just for the challenge. Set in a bohemian enclave of Massachusetts during the summer of 1991, it’s a whisper of a movie about a single mother named Janet (Julianne Nicholson), an open-faced people pleaser who shifts personalities to suit her lovers and friends, and Janet’s guarded 11-year-old daughter, Lacy (Zoe Ziegler), who is obliged to push the interlopers out. With Mom wobbly on her axis, the dour girl’s gravity stabilizes their home.
.
