It's been twenty-eight days now since they arrived. At first we thought they were friendly. It was the Lie groups at first: SO(3) appeared in the sky above Chelmsford, and GL(3,R) blocked the P&O ferry at Rotterdam. The experts said it would stop with the Lie groups, but it didn't. Two days later the vector spaces started appearing, and the day after that it was the differential manifolds. A cornucopia of mathematical objects erupted into the material world.
It was a shock, but, you know, life goes on. People still went to work each morning. Commuters on the M25 zig-zagged around a Hilbert space which was dangling a closed subspace onto the middle lane; transatlantic flights were diverted to Southampton and Bristol when a particularly large non-distributive lattice appeared over Terminal 5 at Heathrow; and the Chelsea v Man United match had to be postponed when a non-commutative C*-algebra touched down at Stamford Bridge.
The mathematical objects appeared at first to be just as inert as they were inscrutable. Some hawkish military types suggested we fire battlefield lasers at them, but, as a strategy, this seemed to rather neglect the fact that the targets in question were abstract, and as such, were invulnerable to assault by packets of mass-energy.
We all got the feeling, however, that we were being watched. Assessed. After ten days, they launched phase two: a firestorm engulfed Swindon on a Wednesday afternoon; the Angel of the North melted like butter in a microwave; and seventy-two telecommunication managers vomited spinal fluid over their PAs. Tectonic tremors shook the major cities of the world. The Earth's magnetic field began to madly gyrate across the globe, green auroral curtains shimmering in the night-sky at equatorial latitudes. Extinct volcanoes lumbered into bellicose life, emetically disgorging viscid flows of lethal magma. And when the Earthquakes and tsunamis came, civilization disintegrated.
I don't know how many of us there are left. We hide in subterranean tunnels and catacombs, where they find it difficult to locate us. We're running out of food and fuel. We have no ammunition which has any effect on them, and we don't understand their motives or capabilities. If you find this message, it's probably already too late.