1. The editor didn’t like the article I wrote for the newspaper. She told me to redo it, so I guess I’ll have to go back to square one
2. The builders constructed a building that didn’t meet the city’s requirements. Now they’ll have to tear it down and begin building again. They’re back to square one.

Synonyms: start from scratch. Compare to: back to the drawing board. Whereas back to the drawing board is used for the idea of re-planning or redesigning, back to square one can apply to starting any activity over. The expression originates from the idea of a game board on which square one is the square where the game begins.