“back to square one”的意思是(因行动失败而)重新开始，退回起点，重头再来，重起炉灶。

【例句】
If your complaint is not upheld, you may feel you are back to square one
如果你的投诉没有得到支持，你可能会感到自己又得重新开始。

If this suggestion isn't accepted, we'll be back to square one.
如果这个建议得不到采纳，我们就得从头再来了。