Theory:

This poem is set on a firework night in the United Kingdom. It is a night where fireworks are burst and celebrated by the whole nation. Colourful bright displays with banging sounds are filled all over the country on such days. Enid Blyton wrote this poem.
  
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Fireworks in full display!
  
The poem is narrated by a pet dog that gets frightened due to the noise of the fireworks. He heard the loud BANG! sound and wondered what the sound was. He again heard the sharp, loud banging noise. He asked his master to listen if he's also able to hear the same. The poor dog thought it was the sound of someone shooting from their guns in the night time. He thought the smaller fireworks were shooting with little guns and the bigger fireworks were from bigger guns. He was very scared and wondered what to do.
 
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The poor dog wondered if the fireworks were gunshots!
  
He called to his master and mistress. He asked them if they heard his cries of alarm. He thought he was in danger. He asked his master and mistress for their help. He wanted them to let him in. He pleaded that he was outside and he wanted to come inside, into the safety of the house. He said before the next firework began he wanted to come in. He said if they shot again with the gun, he cannot bear it. Already his tail had gone down in fright, and his sharp ears had become flat. He was shivering with fright outside the door. He asked his master if they did not like him, as he was suffering outside, and they were sitting inside without taking care of him. He wanted to go inside the house somehow. He tried his best to convince his master.
 
Again there was a banging sound. The dog thought he would die because of his intense fear. He asked his master to let him inside the house for the night, and he said he was so scared that he will die that night itself.
 
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The dog pleaded to let him inside!
  
The master then asked his children, whether they can let the dog in. This line, "(Shall we let him in, children?)" is given in brackets, to indicate that it was spoken by the master, whereas the dog speaks the rest of the poem.
 
The children might have answered "yes" because the door was opened wide immediately. The poor dog ran inside quickly. He felt he was safe inside. There were lights inside the house that made it look magnificent. Outside in the dark, he did not understand what was happening. He became comfortable once he saw the lights and also it was warm. Nights are usually snowy and cold during fireworks night (November month) in the United Kingdom. So the lights provided him with warmth and comfort.
 
He asked his mistress if he could lick her hand. Dogs express happiness, affection and gratitude (thankfulness) by doing such activities. Then he licked her hands and became warm and cosy.
 
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Once indoors, he felt warm and safe!
 
He went behind the big sofa to hide himself from the sounds and dangers outside. He ducked down in a way to defend and protect himself. He asked his owner that he will stay here in this position in safety until the banging sounds were over. He promised to return to his kennel, after the banging sound. Kennels are small shelter houses for dogs, usually kept outside the house, from where the dogs can keep a watch over the house. He said he would return to his kennel to guard them safely throughout the night because they had understood his fear and let him inside. He was loyal and wanted to repay their kindness by guarding them forever.
 
The master and mistress might have been a caring owner to the dog, but have also been careless. They should have taken the efforts to let the dog inside much before the fireworks started, to save him the agony, anxiety of being outside all alone, on a cold fireworks night.
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-8. Firework Night(pp. 141-144). Published by the Tamil Nadu Textbook and Educational Services Corporation.