Star Born by Andre Norton

Raf was two streets away from the circling box but still able to keep it in sight when its easy glide stopped, and, in a straight line, it swooped toward a roof emitting a shrill, rising whistle. It rose again a few seconds later as if baffled, but it continued to hover at that point, keening forth its warning. The pilot reached the next building, but a street still kept him away from the conical structure above which the box now hung.

Undecided, he stayed where he was. Should he go down to street level and investigate? Before he had quite made up his mind he saw the foremost of the alien scouting party round into the thoroughfare below and move purposefully at the cone tower, weapons to the fore. Judging by their attitude, the box had run to earth there the prey they had been searching for.