一个句子的意义往往和上下文有联系，应该结合上下文来理解句义。该句来自厦门大学考试真题2013年试题中的阅读理解。句子上下文如下：Every night she listened to her father going around the house, looking at the doors and windows. She heard the back door closed, she could hear the fastener of the front window click, and the restless pad of his feet going back to try the front door. It wasn't only the outside doors he locked. He locked the empty kitchen too. He was locking something out, but obviously it was something capable of entering into his first defenses. He raised his second line all the way up to bed.

本句前一句的意思是：他要把某个东西锁到外面，但显然这个东西能够突破他的第一道防线。因此，本句的second line是指第二道防线。整个句子的意思是：他将第二道防线直接设置在卧室。