In To Kill a Mockingbird, by Harper Lee, what makes Jem decide to return to the Radley yard the night that Mr. Radley fires his gun?
In Harper Lee's To Kill a Mockingbird, Jem, Scout and Dill go to the Radley house in Chapter Six so the boys can look through the window to see Boo.
Scout is not crazy about the idea, but Jem says she can go with them or leave. This is Dill's last night in town, and she doesn't want to be left out, so she follows along. While Jem looks through a window, there is a shadow on the porch which frightens all three of them away. While they are running, they also hear a shotgun blast, which they believe is aimed at them. To escape, they climb under the fence that borders on the school yard. Jem lifts the fence for the others to climb under. Dill and Scout run ahead and notice that Jem is no longer with them. Returning to the fence, they find that Jem's pants are stuck, and his is kicking them off, leaving them there, and they continue to run.
When the kids return to their house, the adults are gathered outside investigating the commotion of the gun shot. Jem is without pants, which Dill and he explain is the result of playing strip poker at the fish pool. The adults are not happy with this information, but at least the youngsters were not "involved" in the Radley incident (or so the adults believe). Atticus tells Jem to get his pants back. The kids leave and split up.
Jem and Scout go home, but Jem prepares to go out again. He tells Scout that he must return to the fence. If Mr. Radley finds the pants still there in the morning, the word will be out and Atticus will discover the truth of what they were doing—after he warned them twice to leave the Radleys alone. Scout threatens to tell if Jem leaves, but Jem explains that Atticus hasn't had to punish him for a long time, and he wants it to remain that way.
'Atticus ain't ever whipped me since I can remember. I wanna keep it that way.'
So Scout agrees to remain silent, frightened and nervous that Jem will be shot by Mr. Radley when he tries to get his pants. She seems to wait forever, but eventually Jem returns safely. He quietly enters with his pants and climbs—still shaking—into his bed, eventually to fall asleep.
Jem returns to the Radley place that night to retrieve his pants; they had caught on the fence as he, Dill and Scout frantically ran away from Mr. Radley and his shotgun after their latest spying adventure. The most intriguing part of this, to Jem, is that when he returns his pants are neatly folded and hanging on the fence, like someone knew he would be back. The reader can infer easily enough that it is probably Boo, but for both Scout and Jem, the mystery of what goes on in the Radley house only intensifies. Mildly humorous is Dill's explanation to Atticus, when Jem shows up without pants: they were playing strip poker.