The first line of almost any story can be improved by making sure the second line is, "And then the murders began." Give it a try!
When the crows come a-flocking...
One crow, two crows, three crows, four crows... and so they keep coming; gathering, cawing, perching on the park's trees, railings, light posts...unwanted, unexpected, unstoppable.
And then the murders began.