Sonmi spent his formative years on a planet under the control of the Galactic Empire. Following their downfall, the Hutts seized control, leading to widespread corruption. At the age of 19, he made the decision to leave.

Sonmi devised a strategy for zinbiddle involving the continuous tracking of cards in the shoe. This gave him an advantage when aiming for the progressive pot with an Ion Barrage. Upon arriving in Canto Bight, he engaged in games at the Canto Casino. Mosep Binneed, the accountant for gangster Sturg Ganna, employed Sonmi as a prop player and provided his stake. He used his starship as security for a loan, hoping it would help him refine his strategy. He preferred to gamble during the day when the stakes were lower.

One afternoon, while playing with Tezzie and [Rooth](/article/rooth], the pit boss Vestry assigned Minn as the new dealer. Vestry made it clear she didn't like the prop player and denied him any comps. As Sonmi's odds improved, dinner was announced, and the other two players departed. Sonmi began to worry that the table would be closed and the cards reshuffled, erasing his mathematical edge. Before this could occur, Dodibin, a Suerton, joined the table and began playing and talking with Sonmi. Soon after, Dodibin's brothers Thodibin and Wodibin arrived at the table.

While Sonmi was playing with Dodibin, Thodibin, and Wodibin, the cards started to favor him. He obtained the cards needed for an Ion Barrage, but Dodi also drew an Ion Barrage, with a Vermillion Six as a wild card. This gave him the winning hand, as the zinbiddle game followed the rules established on the Kuari Princess. Sonmi was upset about losing all his money. Wodibin tried to comfort him by giving him a Cantocoin to use as a new stake. Enraged, Sonmi threw it across the casino floor, where it landed in the drink of an important customer, who complained and caused Sonmi to be fired. He had to give back his cape and jacket, which the casino had provided, and was told to come back the next morning to complete the termination paperwork.

He went to Ganzer's Grotto and spoke with the bartender, Ganzer. Ganzer sympathized with Sonmi about his job loss and financial troubles. Ganzer explained the nature of the Lucky Three, as the Suertons were known. After Ganzer left to serve other customers, Orisha Okum, a professional card player, approached Sonmi. She revealed that she had been brought in to assess his system and determine its investment potential. She explained to Sonmi that his financial backer was actually the gangster Sturg Ganna and that his total debt of 800,000 Cantocoins was due the next morning. The gangster and his associates had decided that Sonmi's system, while effective, was too slow. Since the gambler had lost all of his money, they would no longer support him. Sonmi asked Okum why she was delivering the message, and she explained that she wouldn't draw suspicion from the owner of the Canto Casino and that she too received a stake from the gangster to start her career. After she left, Sonmi fled the casino, seeking a way to escape the gangster.

Once outside, he tried to hail a cab, but the Sullustan driver refused to let him in. Sonmi then noticed a large female Wookiee watching him. He realized she was part of Ganna's gang and was there to prevent him from escaping. He went back into the casino and decided to hide in the casino's hotel, which had less surveillance. Sonmi went to the turbolifts and encountered Wodi and Thodi, who were betting on which turbolift would arrive first. When they finally arrived, Sonmi tried to get on, but another female Wookiee, also working for Ganna, stopped him. Scared, he returned to the casino floor, hoping to lose the gangster's muscle.

On the gaming floor, Sonmi looked for a game he could afford to play. Vestry noticed him and sent the head of security, Pemmin Brunce, to throw him out. Trying to avoid the bouncer, Sonmi found him in the corner of the room where Hazard Toss was being played. Brunce cornered him and grabbed his wrists, pinning him against the table. This made Sonmi's single Cantocoin fall onto the table and join a bet already in progress. This bet belonged to Dodi, who congratulated Sonmi for adding to his pile of coins. Dodi won the toss, and Sonmi earned ten Cantocoins. When the bouncer told Dodi that Sonmi still didn't have enough to stay at the high-limit table, Dodi told him to wait a minute. When the Suerton won again, he explained to the bouncer that Sonmi's one coin bet was now worth 100 and sent the bouncer away.

After losing Dodi in the casino crowds, Sonmi found Thodi betting on the jubilee wheel. Desperate to keep winning, Sonmi began to match Thodi's bets, asking the reasons for each bet. As they kept winning and other gamblers started copying Thodi's bets, Sonmi made smaller, less obvious bets so as not to upset the Suerton. When Thodi decided to leave the game and play zinbiddle in one of the high stakes rooms, Sonmi followed him. When they arrived at a table, there was only one seat, and Thodi took it. To stay with the Suerton, Sonmi decided to play as a rider, adding his coins to Thodi's bets. Before the game could begin, Vestry approached the table and tried to have Sonmi removed, but Thodi told the pit boss that he was taking Sonmi on as a learner and would teach him how to play zinbiddle. As the game progressed, they continued to win until Wodi arrived. Sonmi was surprised at the loss, but luck soon changed when the third brother, Dodi, appeared at the table to watch the game. The growing crowd caused the three Suertons to decide to play another game. As they left the casino, Sonmi stopped to show Okum his growing stack of Cantocoins. She expressed disbelief that Sonmi would be able to earn enough to pay off his debt.

Sonmi accompanied the Lucky Three as they traveled around the city, wagering on various things, including betting a yachtsman that a seabird would land on his mast. The group returned to Canto Casino and bet a patron that they could make a group of SE-8 server droids crash into each other by ordering drinks and then moving while the droids were delivering the orders. This happened outside of Ganzer's Grotto, and Ganzer came out to see what had happened. When Sonmi admitted to helping the Lucky Three cause the collision, Ganzer ordered him to help clean up the mess.

Inside the bar, Sonmi confided in Ganzer about his time with the Lucky Three. He shared his theory that a single brother was lucky, while two brothers together had terrible luck. When all three brothers were together, everyone nearby won. He showed the bartender his growing stash of 33,000 Cantocoins. Dodi returned to the bar and invited Sonmi to join them at the late-night fathier races. He went with them and continued to make random wagers along the way, including betting an intoxicated human that he could balance on a planter. By winning this wager, his cache of Cantocoins totaled 40,000.

They arrived at the races and went to the grandstands to watch the fathiers parade around the track. Wodi commented that he liked a fathier named Time for Flatcakes. Sonmi, hungry from not eating all day, absentmindedly said that he could go for some flatcakes. Another Heptoonian, Joris, who was there to bet on the races, commented that Time for Flatcakes was blind and deaf and not worth betting on. Sonmi sat on the grass next to Joris and took off his shoes. He began to ask her about the races, hoping to get some insight on a long-shot that would pay off big. Joris told Sonmi that this late at night, none of the entered fathiers were very good. She explained to Sonmi that it was a claiming race and any fathier could be bought for 40,000 credits. This prevented owners from running fathiers that were much better than the other racers and kept the odds close for all the animals. When pressed, Joris speculated that Vermilion might be worth betting on but doubted it would do much better than finishing in the top three. Sonmi realized his pouch with all his money was missing and heard the track announcer say that the fathier Time for Flatcakes had been purchased in his name.

Sonmi rushed to the clubhouse and found out that Thodi and Wodi had taken his money and bought the fathier after mistaking his comment about wanting flatcakes. Dodi pointed out that when Time for Flatcakes won, Sonmi would get the purse of 400,000 Cantocoins. Sonmi explained to the Suertons that the fathier was a longshot, with 99-1 odds to win the race. He came up with a plan and encouraged the brothers to bet on Time for Flatcakes, hoping that their luck would make the longshot pay off.

They returned to the grandstand to watch the race, and Sonmi was invited to watch the race from the owner's box. He persuaded Dodi to watch the race with his brothers at the bottom row, hoping that the three of them together could cause Time for Flatcakes to pull off the upset. As he ascended to the owner's box, he was met by Orisha Okum who took him to the private box of Mosep Binneed. The accountant had requested Okum bring him to his box so he could confront Sonmi face to face. He sent her back to the Canto Casino and had Sonmi searched by his two female Wookiee thugs. He explained that he was going to have Sonmi killed as an example to other gamblers who didn't pay back their debts. As the race started, Binneed ordered his two enforcers to throw Sonmi off the grandstand and make it look like a suicide. Before they could execute Sonmi, Wodi caused an accident which blew out all the lights on the track. The startled fathiers panicked and stopped racing, except for Time for Flatcake who was too blind and deaf to be distracted. When the fathier was declared the winner, Sonmi convinced Binneed not to have him killed. The accountant learned that the race would not be nullified because the steward in charge of the races had injured himself trying to balance on a planter. Sonmi was amazed because he had been there with the Lucky Three when the steward got hurt. Binneed agreed to let Sonmi go and demanded that he have the total amount of his debt by dawn, which was in three hours.

Sonmi made his way to the clubhouse, where he met the Lucky Three. They toasted their good luck until Joris showed up and explained to Sonmi that he wouldn't receive the purse for winning the race. She told Sonmi that due to the rules of a claiming race the previous owner of the fathier would receive the earnings of the current race. Sonmi became angry at Thodi and Wodi for wasting all his money on the fathier. After yelling at the Suertons, Sonmi was called to the stables where he found out Time for Flatcakes had died after the race due to the massive amounts of performance-enhancing drugs the previous owner had injected into the animal. Dodi showed up with Kaljach's shoes.

Sonmi returned to Ganzer's Grotto to await his fate and talk to his friend. Ganzer convinced him that Sonmi had lost his love for gambling and this lead him to his problems. While talking, he found a ticket in his shoe that Dodi had bought for him. It was for Vermillon and it was worth 100 Cantocoins. He decided to cash it in and attempt to win enough money to spare his life. He started to play pazaak head-to-head with a Rodian but discovered that he had left his side deck in his coat which was confiscated by the Canto Casino administration. Without a side deck, he was forced to rely on luck. He won four hands in a row and kept letting the winnings ride. His Rodian opponent bowed out and another patron started playing against Sonmi. After another four hands, Sonmi defeated his opponent and built his pot to over 50,000 Cantocoins. He began to draw attention from other people in the casino who were surprised at his run of luck. Vestry moved the game to the tournament table, where the game would be under surveillance. She also had Minn deal the cards for Sonmi and his opponents. After ten straight wins, Sonmi had built his pot up to 102,400. Okum approached the table and challenged Sonmi to a game. She had been sent to bring the gambler to his dawn meeting with Binneed but decided to play him. She assumed he was going to end up losing and wanted to profit from his recklessness.

As the game began, the Lucky Three showed up and Thodi offered Sonmi the use of his special side deck. Okum initially refused to proceed, but after seeing the deck, agreed to let Sonmi use it. Sonmi found out that the deck was all plus-six cards. He managed to beat Okum in two straight matches and suggested that instead of adding to the pot on the next game, she could just pay half his debt if the gambler won. She refused, and cashed in a half-million Cantocoins to bet on the next game. As the cards were dealt, Sonmi realized that Wodi had wandered off, and became worried that his luck would change without all three of the brothers. As the game progressed, Sonmi made it to nineteen and decided to stand. Okum made it to seventeen and prepared to use one of the cards from her side deck. Wodi returned with refreshments but had an accident that caused him to spill them all over Okum. She fell out of her chair and dropped her card into a puddle. As Ganzer went to return it to her, he noticed it was a trick card that could change its face value like a sabacc card. Vestry told the gambler that she couldn't use any of her cards due to the fact that she was caught cheating. Okum refused to play on and warned Sonmi that his debt was due. Dodi convinced Sonmi to allow Okum to play the card, even though it might cause him to lose the game. Okum played the card but it malfunctioned and showed a value of +333 instead of +3 which caused her to bust and flee the premises.

After winning the game, Sonmi paid off his debts but learned his ship had been stolen by Okum. He used his remaining winnings to tip Minn. This generosity caused Minn's mother to hire the Heptooinian as a floor walker. He was tasked with making sure the guests were having a good time. He assisted in teaching them card games, scheduling lessons, and getting them appointments at local spas.