Theory:

Ruskin Bond is the author of the story. He explains in this story how his grandfather's habit of upbringing animals had once landed him in trouble. Since the narrator's grandfather was interested in buying a monkey, he bought it from a tonga-driver; and it cost around five rupees. The tonga-driver had not allowed the monkey freely but tied it around the feeding trough. It made the monkey feel so uncomfortable. When Grandfather had bought the monkey, he decided to put it into his private zoo.
 
The writer or the narrator hints here that his grandfather had his private zoo, reflecting his passion for animals or birds.
Toto was the name of a monkey, and it looked so pretty. As the narrator's grandfather was interested in upbringing the animals or birds, he might have bought Toto. His mischievous eyes twinkled under deep-set brows. His pearl-like white teeth and his deep smile looked frightening enough to scare elderly Anglo-Indian ladies.
 
Toto’s scary smile.jpg
Toto’s scary smile
 
Though Toto looked pretty with gleaming eyes and a scary smile, the narrator says Toto's hands seemed too dry, like being pickled on the sun for years together. Still, the narrator admires Toto's hands and tail.
The narrator also points out that his grandfather always prefers supporting a tail linking to one's good look. Moreover, the tail can also be like a third hand to help. The narrator's grandfather also believed that it could hang from a branch; pick up any delicious fruit or food items that could not reach through Toto's hands.
 
If the narrator's grandfather is interested in running a private zoo, his wife is not supportive and has a particular viewpoint on raising animals or birds. Since the narrator's grandmother disapproves of her husband taking any new bird or animal into the house, he wishes to keep Toto's arrival a secret.

Grandfather had decided to let his wife know about Toto when she was in a good mood. So, the narrator helped his grandfather to keep Toto secretly in his bedroom wall closet. Since Toto would not remain in the same place, they safely tied it to the peg attached to the wall. After a few hours, when the narrator and his grandfather returned to the narrator's room to release Toto, they found many messy things happened over there.
 
Toto inside the narrator’s room.jpg
Toto inside the narrator’s room
 
Toto had damaged the entire room. It had torn the fancy wallpapers that were chosen by his grandfather. The walls looked empty without those wallpapers. The worst part is, Toto broke the hook on which the narrator's blazer was hanging and tore it too.
 
When the narrator was concerned about Toto's activities, he noticed that it had no effect on his grandfather. He appreciated Toto's work.
 
The narrator's grandfather did not scold Toto or feel guilty for putting Toto in his place. Despite this, he praised the monkey's work and said, "He's clever". Furthermore, he said that if they had given more time to the monkey, it would have made a rope by attaching the torn pieces of the narrator's blazer and escaped through the window.
 
Even then, the narrator's grandfather said nothing about Toto's existence in their home. Toto had been moved into a large cage by the narrator's grandfather. The cage was in the servants’ quarters. It was in that cage where the grandfather's collection of pets lived.
 
Toto on a big cage.jpg
Toto inside the big cage
 
His collection includes a tortoise, two rabbits, a tame squirrel, and the narrator's pet goat. In the night, the mischievous monkey did not allow his fellow animals to sleep.
 
Since the monkey was disturbing the other animals, the narrator's grandfather did not allow Toto to remain in the pet's cage. On leaving Dehra Dun, he took Toto with him on his way to Saharanpur. He travels to Saharanpur to get his pension.
 
Toto joined the narrator's grandfather on his journey. Unfortunately, the narrator was unable to accompany his grandfather that day. Nonetheless, his grandfather explained what happened during the journey. The grandfather gave Toto a large canvas kit bag; the bag was black.

The kit-bag turned into a temporary home for Toto; it was arranged with straw in the bottom for the Toto to live. Grandfather closed the bag so that Toto would not escape from it as he was aware of Toto's naughty misbehaviour.

Toto couldn't get its hands outside as the bag was closed, and it couldn't tear or bite the bag because the fabric was so strong. Toto's constant attempts to get out of the bag resulted in the bag rolling on the floor and some times jumping into the air. Toto's attempts to get out of the bag were amusing and drew onlookers' attention on the Dehra Dun railway platform.
 
As a mischievous monkey, Toto tried hard to get out of the bag. As he had set things in a way that Toto couldn't come out, it struggled hard pushing to come out of the bag.

It remained in the bag until Grandfather provided his ticket at the Saharanpur railway gate but suddenly popped his head out of the bag and gave the ticket-collector a broad smile. The narrator's grandfather was irritated as his efforts in keeping the monkey secret had failed, and the ticket collector was greatly shocked by the monkey's appearance.

The funny thing about the ticket-collector was, he thought it to be a dog and so demanded the pay according to the norms of the railway department for Toto. Finally, grandfather's efforts in keeping Toto secret in his bag failed at last. His attempts to prove to the ticket collector that Toto was a monkey and not a dog become unsuccessful. He tried hard to make the ticket collector understand that it was not even a four-foot animal. Finally, grandfather had paid three rupees charge for Toto's ticket too.
Grandfather was annoyed by the ticket collector's behaviour and was unhappy with the three rupees he had paid for the monkey. He took out his pet tortoise from his pocket, angry, and asked the ticket collector if he charges for that as well. The ticket collector paid close attention to the tortoise and pressed his forefinger against it to examine the creature's type.

After inspecting the tortoise, he smiled at grandfather and said that no ticket was issued because it was not a dog. Nonetheless, grandfather had been concerned about paying three rupees for the monkey's ticket.
 
When the narrator's grandfather returned home from Saharanpur, it seemed that his grandmother had known about Toto. Nothing as bad had happened as Grandfather had predicted. Toto was given a position in a stable after Grandmother accepted his presence in their house. Grandfather kept it with their family donkey, Nana, because Toto wouldn't let other animals sleep through the night.
 
Nano.jpg
Nana
 
Since grandfather was aware of Toto's naughty behaviour, he visited Toto's place to see if it was comfortable. He also wanted to see if Toto was okay with being around their family donkey. He then noticed that their family donkey, Nana, was skipping meals by standing away from the hay bale for no apparent reason.
 
When grandfather noticed Nana skipping its food, he gave it a slap across the haunches. Nana jerked backwards, pulling Toto with it when Grandfather hit it around the haunches.
 
Through Toto's pointed little teeth, it had held tight to Nana's long ears. Grandfather's expectations never fulfilled as Toto and Nana did not become friends anymore.
 
During the cold winter evenings, a special treat awaited Toto regularly. It was nothing but a large bowl of warm water. Toto loved the big bowl of warm water offered by the grandmother for a bath on cold winter evenings. Still, Toto would check the temperature with his hand, then slowly walk into the bath, first one foot, then the other as it had seen the narrator doing so. Then it will immerse into the warm water until it was up to his neck.
 
When Toto ultimately gets inside the water and makes itself comfortable, it will take soap in his hands or feet and start rubbing all over his body. It will remain in the water until it is warm. Once the water gets cold, quickly it comes from it. It would then make its way to the kitchen to dry itself with the kitchen flames.

Toto would love the bath session every time, and if anyone laughed at Toto during this session, Toto would refuse to proceed with his bath. The author has provided a detailed, humorous narration of Toto's bathing style in this paragraph, allowing the reader to envision and appreciate the monkey's bathing style.

Days passed. One day, Toto came dangerously close to being burned alive. The grandmother kept a big kitchen kettle on fire to prepare tea. Toto got into it by opening the lid, thinking it was prepared for its bath. Unfortunately, when Toto opened it, the water was warm enough to take a bath.
 
When the water was only lukewarm when Toto got into it, the fire underneath the kettle gradually increased the water to boil. When Toto sensed something wrong, it wanted to come out but sat back due to the cold weather. As a result, it hops up and down for an extended period before the narrator's grandmother arrived.
 
When the narrator's grandmother saw Toto on a boiling water kettle, she rushed and carefully pulled Toto from the boiling water. Toto was almost half-boiled in the kettle's boiling water.
 
The narrator exaggerates Toto's biological design or nature while describing Toto's mischievous deeds. He says, if there is anything like a portion of the brain dedicated explicitly to mischief, it was significantly developed in Toto.

Toto was constantly tearing things apart. When the narrator's aunt approached Toto, it grabbed her dress and tore a hole in it. One day at lunch, a large dish of pullao was set in the centre of the dining table. When the narrator's family entered the room, they were shocked to see Toto was stuffing itself with rice.
 
Toto on the dining table.jpg
Toto on the dining table
 
When the narrator's grandmother screamed at it, Toto threw a plate at her. One of the narrator's aunts ran up to Toto and was hit in the face with a glass of water. Toto picked up the pullao dish and left through a doorway while the narrator's Grandfather approached the dining room. Nobody could keep Toto under control.
 
It moved to the top of the jackfruit tree, keeping the pullao dish in its hands. It didn't come down the tree but stayed there all afternoon.
 
Monkey on a jackfruit tree.jpg
Monkey on a jackfruit tree
 
The narrator's family noticed Toto taking his time finishing the pullao. It might be that the pullao had been so tasty to Toto's tongue that it didn't waste a single grain and ate everything.
 
In the end, to punish the grandmother who had screamed at him, it threw the dish from the tree, giggling with delight as it dropped into a hundred pieces.
 
Toto’s revenge on grandmother.jpg
Toto’s revenge on grandmother
 
Grandfather happily brought Toto to raise, but things did not go as planned. He finally realised that Toto, like his other pets, couldn't be kept at home. Grandfather initially liked and appreciated its activities. He was never against Toto and hated him, but he quickly realised Toto's nature.
 
The mischievous Toto.jpg
The mischievous Toto

The narrator also makes a valid argument here, stating that, while the narrator or his grandparents did not hate Toto, they couldn't afford to replace items like plates, curtains, and wallpaper regularly since they do not come from a wealthy family.
 
Finally, the narrator's grandfather decided to take Toto away from their house. He was able to track down the tonga-driver and sold him, Toto, back for just three rupees as he somehow wanted to get Toto out of their home.