On the map of the living point that Zhang Xu withheld under various pretexts, a total of seven secret passages leading to Hogsmeade were drawn.

According to the Weasley twins, Filch knew four of them, and the twin brothers knew the other three, including the one that had collapsed a few years earlier.

And this Death Eater's sneak attack was the one that was blocked because of the collapse.

In Dumbledore's map, there are four other paths that lead to the depths of the forest, and one that leads directly to the bottom of the lake.

Considering the period in which Hogwarts Castle was built, it's not surprising that there were so many escape routes.

Dumbledore estimated that the headmaster's map, which had been passed down from generation to generation, did not include all the secret passages.

On the map provided by Dumbledore, there was only one secret passage to the Forbidden Forest that could be used, and the rest collapsed.

The inside of the secret passage leading to the bottom of the lake is fine, but the exit from the bottom of the lake is blocked with stones by unsuspecting fish.

Of the four secret passages that Filch of Hogsmeade knew, three more had collapsed in the past few years, and only one was left to use.

In other words, Zhang Xu needs to set traps in the three tunnels leading to the Forbidden Forest and the four tunnels leading to Hogsmeade.

After Zhang Xu explained to Dumbledore the design ideas and principles of his trap, Dumbledore immediately approved his plan.

It's just that Zhang Xu has limited materials at hand now, and he can only set up a trap for a secret passage today, so Dumbledore asked him to set a trap in the secret passage that the Death Eaters used last night to prevent the Death Eaters from using this secret passage again.

After coming out of the principal's office, it was already dinner time, and Zhang Xu, who was already hungry, walked towards the cafeteria.

Today is the last day of the Christmas break, and all the Hogwarts students have returned to school, and everyone is in the cafeteria discussing the harvest of the holiday while waiting for dinner to begin.

However, the news of the sneak attack on Hogwarts last night quickly spread from Peeves to the students.

The incident quickly caused an uproar among the students, and with the news of Azkaban's escape from prison in the Daily Prophet today, various rumors began to circulate among the students.

Zhang Xu found Fred and George, who were chatting with their classmates at Dean Lion's desk, stuffed a parchment note into the two of them, and said, "When there is a difference between ten minutes and eight o'clock tonight, take this to Filch's office to find him." ”

Then he ignored the bewildered twin brothers and walked straight back to the long table in the Eagle Courtyard to eat.

Fred and George arrived at Filch's office on time, and Filch handed a huge toolbox to the two of them after reading Zhang Xu's note.

After picking up a box of tools and materials for filling holes in the wall from Filch, the twins followed Filch's instructions to the mirror on the fifth floor.

At this time, Zhang Xu and Peeves were already waiting here.

Zhang Xu beckoned the twin brothers to follow, and then led the two of them and Peeves into the secret passage behind the mirror on the fifth floor.

The reason why Fred and George were brought to help today was because they were familiar with the secret passages, and on the other hand, it was also to remind them that the Death Eaters would not be killed, but would have killed these two people who liked to drill through the secret passages.

It is not an exaggeration to describe the secret passage of Hogwarts with nine turns and eighteen turns, and after walking many roads and descending a few stairs in the secret passage, Zhang Xu and Peeves finally came to the collapsed place.

Along the way, Zhang Xu told the twin brothers everything that happened last night, but concealed the fact that the Death Eaters were led by Snape.

Both Fred and George were taken aback when they learned that the Death Eaters had infiltrated Hogwarts with their invention of rat cookies.

"The shape-shifting cookies you sell in the future can shorten the effective time to less than one minute." Zhang Xu said to the two of them.

At this time, they had already walked to the obstacle, Zhang Xu pointed to the half-collapsed hole and said, "If their transformation time is less than a minute, maybe they will be stuck in the hole." ”

The secret passages of Hogwarts are all made of stone, and they are quite strong, but they have not been maintained for hundreds of years, and it is inevitable that they will collapse in some places.

At the site of the collapse in front of me, the stone slab at the top of the secret passage was crushed by a large rock and dirt underneath.

A huge rock is located just above the secret passage and is not discovered, which is very dangerous in tunnel construction. Because the boulder in the dirt is invisible, when the earth underneath the boulder is hollowed out, the boulder can easily collapse the tunnel under the action of gravity. Such a case can write a history of blood and tears in tunnel construction.

It now appears that the use of magic in the construction of the secret passage at that time caused the boulder to collapse the secret passage hundreds of years later.

Zhang Xu observed the hole where the Death Eaters had come for a while, and found that this side of the boulder was slanted, and the upper part was covered with dirt, and the back half of the cave was stone, and the front half was dirt.

By the time the Death Eaters had gotten in, this section of the dirt had collapsed considerably.

Zhang Xu stabbed the surrounding dirt a few times with his wand, making it look like it had collapsed naturally and plugged the hole.

After all, Shenfeng can only drill holes, and cannot strengthen the cave walls.

Zhang Xu looked around again and found that the collapsed boulders and mud blocked the secret passage tightly.

After inspecting the scene, Zhang Xu began to arrange the task.

"Peeves, look up all the vents from here to the previous corner."

"Fred, George, after Peeves finds the outlet, seal them all up, preferably so that you can't see any traces in the secret passage."

The twin brothers had no objection, and began to block the vents together with Peeves according to Zhang Xu's instructions.

The vents in the passages are very hidden, but with the presence of Peeves, who makes a cameo appearance as the Dirt Walker, he can quickly find the vents through the ventilation ducts in the dirt.

After Zhang Xu walked to the first corner and chose a place, he drilled a wrist-thick hole in the stone slab at the top of the secret passage, and then conjured a herringbone ladder, climbed up and stuffed a piece of C4 into the hole, and then inserted a detonator and fuse.

After estimating the place where the new collapse in the secret passage could not be affected, Zhang Xu took out a gas canister from the treasure bag and put it there.

Wait until all the vents are blocked, and then blow up this secret passage, this section of the secret passage will form a confined space, and this tank of gas that has just been changed on New Year's Day is enough to turn this place into a gas chamber.

The foul smell that had accumulated over the centuries in the tunnels should have made the Death Eaters ignore the foul smell of ethyl mercaptan in the gas.

It's just that for a period of time in the future, when I was too lazy to run to the kitchen, I couldn't secretly cook and eat by myself in the dormitory.

According to the working rules of house-elves, it is okay for them to send food to the professor's office and the professor's dormitory, but not to the public dormitory.

A trap is that the simpler the better, simple sometimes means fewer flaws, and fewer flaws mean that they are difficult to find.

It would have been nice if the Death Eaters had smoked another cigarette to calm down.

After the twins and Peeves blocked all the vents, Zhang Xu lit the long fuse, and then led everyone to run vigorously.

After a loud "boom", the shock wave rampaged through the secret passage, but fortunately, Zhang Xu added a shield to everyone, so except for being shocked by the loud sound, everyone was fine.

After the dust settled, Zhang Xu and the others returned to the explosion site and found that this secret passage had been blown up, and the mud and stones had blocked this section of the secret passage.

After checking that there were no gaps that would cause air leaks, Zhang Xu let Peeves pass through the obstacle and unscrew the valve of the gas tank opposite.

After Peeves' return, Zhang Xu left the secret passage with them.

Zhang Xu estimated that he had to buy a lot of bottles of carbon monoxide in the Muggle world to be enough, after all, the bottles could not be brought out with this method, and the odorless carbon monoxide was more hidden than the gas with the addition of ethyl mercaptan.