捷达车驶离工农村，吴敏打开收音机，里面正播放着英语新闻。“Listen，”她调大音量，“This reporter is talking about solving old cases. What tense did she use？”（听，这个记者在讲破获旧案，她用了什么时态？）

刘念初侧耳听着：“Past perfect. She said ‘The police had searched for clues for 30 years before they found the evidence.’”（过去完成时。她说“警方找了30年线索，才找到证据”。）

“Exactly.”吴敏点头，转动方向盘拐上高架桥，“Your grandpa would be proud of you. He used actions to solve cases, and you use knowledge to understand them.”（没错。你爷爷会为你骄傲的，他用行动破案，你用知识理解案件。）

和平路的梧桐树投下浓密的树荫，塘沽一中的红砖墙外，穿白色校服的学生正陆续走出校门。张路岑抱着练习册站在桂花树下，看到刘念初立刻挥手：“Nianchu！Here！”（念初，这里！）

“Long time no see！”（好久不见！）刘念初走过去，把布包递给她，“Wu laoshi asked me to give this to your mom. She said your English composition is getting better.”（吴老师让我把这个给你妈妈，说你英语作文进步了。）

张路岑眼睛一亮，刚要说话，远处突然传来警笛声。几辆警车停在街角的老邮局门口，沈砚舟正指挥警员拉起警戒线。“What's happening？”（发生什么了？）张路岑好奇地问。

刘念初的心沉了一下：“I need to go there. See you later！”（我得过去看看，回头见！）

警戒线内，拆弹专家正小心翼翼地拆解一个铁盒子。“The lock is triangular，same as your grandpa's ruler！”（锁是三角形的，和你爷爷的尺子一样！）顾野举着相机，用刚学的蹩脚英语喊。

刘念初掏出铜三角尺，插进锁孔轻轻一拧，“咔哒”一声，盒子开了——里面是叠泛黄的物理试卷，最上面一张写着“Li Minghao”，日期是1988年9月。

“His dad was a policeman who died in 1988.”（他爸爸是1988年牺牲的警察。）沈砚舟看着试卷上的泪痕，“The note says his mom sent the papers to the school, hoping teachers would encourage him.”（字条说他妈妈把试卷寄到学校，希望老师鼓励他。）

吴敏不知何时也走了过来，看着那些空着的大题，轻声说：“He couldn't focus on studying because he missed his dad. Just like you sometimes can't concentrate on homework when you think of your parents.”（他因为想念爸爸，没法专心学习。就像你有时候想起父母，也会写不进作业。）

“Mom，”刘念初转头看着她，眼眶有些红，“I think we should find him and tell him his mom's love didn't disappear.”（我想我们该找到他，告诉他妈妈的爱没有消失。）

吴敏点点头，握住她的手：“Let's go to the teaching research meeting first. After that, we'll buy osmanthus cakes. Your grandpa used to say, ‘Sweet things make people forget sadness.’”（先去开教研会，结束后买桂花糕。你爷爷说过，甜的东西能让人忘了难过。）

远处的桂花树下，张路岑、黄晨和刘冠辰正朝她们挥手。刘念初看着手里的三角尺，忽然觉得英语课上学的过去完成时，就像这把尺子——能丈量出那些“已经发生”的故事里，藏着多少未说出口的爱。

她知道，新的案子还在等着，但身边有会用英语讲证据的吴妈妈，有记着她的老朋友，这就够了。就像工农村的职校和和平路的高中，虽然隔着老远，却被同一片阳光照着，暖烘烘的。