Theory:

     After an hour the rain stopped, and although the wind continued to blow, it was now taking the clouds away, so that the thunder grew more distant. Then the wind too moved on, and all was silent. Towards dawn the whistling-thrush began to sing. Its sweet broken notes flooded the rain washed ruins with music.

     ‘Let’s go,’ said Usha.

     ‘Come on,’ said Suresh. ‘I’m hungry.’
 
     As it grew lighter, they saw that the plum tree stood upright again, although it had lost all its blossoms. They stood outside the ruins, on the brow of the hill, watching the sky grow pink. A light breeze had sprung up.

     When they were some distance from the ruins, Usha looked back and said, ‘Can you see something there, behind the wall? It’s like a hand waving.’
Explanation:
 
After almost an hour, the rain stopped, but the wind continued to blow and took the clouds away, so there was no thunder. Slowly the wind also was not there, so everything was calm. The whistling-thrush bird began to sing again, and it was so sweet that the ruins were full of music now.
 
Usha asked if they all can start.
 
Suresh was still hungry, so he was reluctant to walk.
 
Sometime later, they saw the plum tree again though there were no blossoms, but it stood straight once again. They all stood outside the ruins watching the sky, which has turned pink. There was a slight breeze now.
 
They started towards the village after sometime when Usha turned back to the ruins she asked others if they could see something on the wall, maybe a hand waving.
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
Brow
Peak, tip.
2.
Sprung Leap, jump.
3.
Whistling-thrush A type of a bird.
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-7. The Wind on Haunted Hill by Ruskin Bond  (pp. 25-34). Published by the Tamil Nadu Textbook and Educational Services Corporation.