A possible concise summary is:
Two people visit their grandmother's house, hoping to inherit it, but they discover that she is a violent and murderous person who has set up traps and weapons all over the place. They try to escape from her by finding keys, tools and secret passages, but they encounter many dangers and obstacles along the way. They manage to hide in a playhouse, but they are still not safe from their grandmother's wrath.
Here are the key facts extracted from the text:
1. The narrator receives a letter from someone claiming to be their grandmother, inviting them to visit.
2. The narrator is hesitant at first, as they have bad memories of their grandmother.
3. The narrator decides to visit, hoping to inherit their grandmother's house.
4. The narrator and someone else, possibly a friend or companion, arrive at the house and begin to explore.
5. They discover that the house is full of traps and defenses, including a guillotine and tranquilizer darts.
6. The narrator's companion is injured after triggering a trap.
7. The narrator finds a crossbow and tranquilizer darts, which they plan to use to defend themselves against their grandmother.
8. The narrator and their companion try to escape through a secret passage, but it leads to a dead end.
9. They find a well and a cradle, which the narrator recognizes as belonging to their mother.
10. The narrator finds a hammer and uses it to detach boards from a door.
11. They discover a playhouse in the courtyard, which the narrator remembers as a place they used to hide from their grandmother.
12. The narrator and their companion enter the playhouse, hoping to find a way to escape.
13. The narrator's grandmother is heard outside, trying to get in.
14. The narrator and their companion try to come up with a plan to escape, knowing that their grandmother will be more aggressive now that she knows they're in the playhouse.