A couple confined to a small space turns their garden into a make-believe pub for the birds and squirrels, and then has to keep it running through a freezing winter. The speaker mentions that "the world got stopped," which suggests a time of restriction, though the poem never names the cause. The garden feels like a lucky find, and the tone is playful: the animals are "punters," the dish of water is a bar, and the whole place is called The Grain & Shell.
The mood shifts when the water in the shell freezes. Birds can't break through the ice, and squirrels leave disappointed. So every morning the speaker boils a kettle, melts the ice, and watches it steam, taking care not to scald anyone. It's a small, daily act of kindness.
The ending is quiet but stubborn. "Nevertheless we do persist" and "It will get warmer" can be read as being about more than the garden. The feeling is gentle, hopeful, and a little weary.