‘The Spitfire Grill’

A single convincing performance can elevate an imperfect movie, which is what Alison Elliott’s (left) graceful acting does for “The Spitfire Grill.” Elliott’s performance, strong in and of itself, also considerably raises the usual level of co-stars Ellen Burstyn and Marcia Gay Harden (right) (Showtime Friday at 8 p.m. and Saturday at noon).