Mia, Protector of the Realm.
The other night, I had just gone to bed. Mia, as usual, was sprawled across my ankles. I was almost asleep when she bolted upright, pushed off hard and leapt off the bed, headed for the hallway outside the bedroom, and let loose with a long, low growl of a moan.

This sound gets me wide awake, because it's usually the precursor to the production of a hairball, and I know I've got about seven seconds to turn on the light, put on my glasses, find a newspaper or magazine, and thrust it under Mia's head, in hopes that it lands up on the paper instead of the rug. (As an aside, Mia's champion hairball was about nine inches long. Amazing what a long-haired cat can produce.)

When I turned the light on, to my surprise I saw that Mia wasn't in an imminent-hairball-production pose; she was crouched and ready for a fight. And she was staring down the Outdoor Cat, who had somehow gotten out of her bedroom and was innocently exploring the upstairs. Mia was controlling the situation, although I had the feeling that we were about eight seconds from full-scale hissing and twelve seconds from a scratching fight, which Mia would lose, much to her surprise (as she's been declawed and Outdoor Cat has not).

I got between them - at great risk to my legs - and picked up Outdoor Cat, and returned her to the bedroom/prison she shares with her kittens.

Mia got a reward - a piece of cheese - and slept very soundly, as her job was complete.