We knew our parents wouldn't let us travel alone, so we had to invent a story to avoid them realizing what happened.

invent 是动词，意思是"发明、创造"，在这里引申为"编造、虚构"故事。这个词来自拉丁语 inventus（发现），由 in-（进入）和 venire（来）组成，原意是"发现、找到"，后来发展出"创造新事物"的含义。