My mother was about to die from her agony while my father was trying to find a way to lock me in.

lock 是动词，意思是"锁上、关住"，指用锁或其他方式使门、容器等无法打开。 in 在这里是副词，表示"在里面、进入"的状态。 lock in 这个短语动词表示"把某人锁在里面"或"限制某人的自由"。