Lum, Ataru, Megane & Co. are holding a party to celebrate the 1st anniversary of her arrival on Earth. After Ataru openly gripes about his life with Lum, she gets up and leaves. She can't be found, and it's feared she's left Earth for good.
Lum's alien friends keep popping up at school, and disappearing right before Lum can have a chance to talk to them. Now her feelings are hurt because she feels she's being left out of whatever they're doing.
Lately the students of Tomobiki H.S. have been sneaking off campus to eat at the local eateries, and the faculty, led by Onsen, is conspiring to stop them at all costs. It's all-out war, with restaurant district as its battlefield!
Ten brings a huge cat home with him, and he takes an immediate liking to Ataru's kotatsu (foot warmer), and sits on the staircase with it. It's dinnertime, and Ataru can't come downstairs to eat without getting pummeled by that darn cat.