因為：midnight 是午夜時分，即零點前後。
所以：按日期時間的介詞使用規則而言：in 明顯不合適了哈。
Whoever in the forest is hardly seen at midnight, especially the person with a dark green coat.
2、但 in the midnight 則也是正確的。
He was seen going quickly through that lane in the midnight yesterday, so that the cop suspects him isn't surprising at all.