Here’s the face of someone who’s just thrilled to be wearing a trash bag. (Fox)

A lady is trying to teach her dog to say “milk.”

“Milk. Milk. Come on, you can say it, milk,” she says. The dog peers at her with puzzled eyes. “All right, that’s enough for today,” she tells him. “But mark my words: You will talk.”

He doesn’t. And there’s nobody else for her to talk to. A plague has wiped out virtually every other living being, and she’s alone in a bunker with her canine pal, drowning her sorrows in booze and dining on cat food because that’s all that’s left to eat.

The dog story unfolds in the midseason premiere of “Last Man on Earth” (Fox, Sundays at 9:30 p.m.), which aired earlier this month. The lady (played by the incomparable Kristen Wiig) is loopy socialite Pamela Britton, a new character. Instead of picking up the narrative from the first half of Season 3, “Last Man” offers her standalone story — and gives us a glimpse of how the virus swept the planet. Britton and her husband watch cable news in disbelief as hearses carry away the remains of departed presidents Mike Pence, then Paul Ryan, then Rex Tillerson, all the way down the cabinet to Betsy DeVos. Then the husband begins to spit up blood — the first sign of impending death. So Pamela and her pooch flee to a bunker.

Wiig, with her genius for finding the pathos in comedy and the yuks in tragedy, is brilliant as always, protecting herself from germs by dressing in garbage bags (accessorized with a lovely gold belt). Three years into her bunker stay, her personal drone discovers a group of survivors — the cast of “Last Man” — and she musters the courage to go search for the remnants of humanity.

Where does the wildly inventive “Last Man” go from here? Last night’s show was not available for preview before I filed this column, because series creator and star Will Forte is that secretive. Rumor has it that Wiig will be in several episodes, which is heartening news. Because I want to see more of a woman who looks at a can of refried beans in the bunker pantry and wonders, “Why didn’t they fry ’em right the first time?”