Sonmi grew up on a planet ruled by the Empire. When they were defeated, the Hutts took over the planet and it descended into widespread corruption. He left when he was 19 years old.
Sonmi developed a system for Zinbiddle where he kept a running count of the cards in the shoe so that he would have favorable odds at winning the progressive pot with an Ion Barrage. He arrived on Canto Bight and played at the Canto Casino. Sonmi was hired as a prop player and was staked by Mosep Binneed, who was the accountant for the local gangster Sturg Ganna. He used his starship as collateral for a loan that he hoped would allowed him to perfect his system. The gambler mostly played during the day, when the stakes were lower.
He was playing on a early afternoon with two other patrons, Tezzie and Rooth, when the pit boss Vestry assigned the new dealer Minn to the table. Vestry also expressed her dislike of the prop player, forbidding him from getting any comps. As the odds turned into Sonmi's favor, dinner was announced and the other two players left. Sonmi began to panic, fearing the table would be closed and the decks reshuffled. This would eliminate the mathematical advantage that the gambler was working on. Before this could happen, the Suerton Dodibin sat down at the table and started playing while conversing with Sonmi. Soon after, Dodibin's brothers Thodibin and Wodibin showed up at the table.
Sonmi was playing with Dodibin, Thodibin, and Wodibin when the cards turned into his favor. He got the necessary cards to get an Ion Barrage, but Dodi also drew an Ion Barrage, with a Vermillion Six as a wild card, which made his hand the winning hand since the zinbiddle game was governed by rules formalized on the Kuari Princess. Sonmi became upset at losing all his money. Wodibin attempted to calm him down by giving him a Cantocoin as a new stake. Sonmi, enraged, threw it across the casino floor and it landed in the drink of an important customer who complained and got Sonmi fired. He had to turn in his cape and jacket, which were provided to him by the casino, and was ordered to return the next morning to fill out the paperwork to finalize his firing.
He went to Ganzer's Grotto and talked to the bartender Ganzer. He commiserated with Sonmi about the loss of his job and money. Ganzer explained the nature of The Lucky Three, as the Suertons were known. After Ganzer left to attend to some customers, Sonmi was approached by Orisha Okum who was a professional card player. She explained that she was brought in to look at his system and see if it was worth investing in. She explained to Sonmi that his financial backer was really the gangster Sturg Ganna and that his total debt of 800,000 cantocoins was due in the morning. The gangster and his associates decided that Sonmi's system, while effective, was too slow and since the gambler had lost all of his money, they would no longer support him. Sonmi questioned Okum on 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 to look for a way to escape the gangster.
Once outside, he attempted to get into 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 watching him to prevent him from fleeing. He re-entered the casino and decided he'd try to hide in the casino's hotel, which had less surveillance. Sonmi went to the turbolifts and ran into Wodi and Thodi who were betting on which turbolift would arrive first. When they finally arrived, Sonmi attempted to get on but was met by another female Wookiee who was also working for Ganna. Frightened, he went back to the casino floor in an attempt to lose the gangster's muscle.
On the gaming floor, Sonmi attempted to find a game that he could afford to play. He was noticed by Vestry, who sent the head of security Pemmin Brunce over 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 caused Sonmi's single Cantocoin to fall on the table and join a bet already on the table. 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, and when the Suerton won again he explained to the bouncer that Sonmi's one coin bet was now worth 100 and sent the bouncer off.
After losing Dodi in the crowds on the casino floor, Sonmi found Thodi who was betting on the jubilee wheel. Desperate to keep winning, Sonmi started to match Thodi's bets, while asking the reasons for each bet. As they kept winning and other gamblers starting matching Thodi's bets, Sonmi made lower paying tangential bets as to not upset the Suerton. When Thodi decided to leave the game and go 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 make sure he could stay with the Suerton, Sonmi decided to play as a rider, adding his coins to Thodi's bets. Before the game could start, Vestry approached the table and tried to get Sonmi removed but Thodi told the pit boss that he was taking Sonmi on as a learner and teach him how to play zinbiddle. As the game progressed, they kept winning until Wodi showed up. Sonmi was surprised at the loss, but luck soon changed as soon as the third brother, Dodi, showed up 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 her disbelief that Sonmi would be able to earn enough to pay off his debt.
Sonmi tagged along with the Lucky Three as they traveled the city, making wagers on various things including betting a yachtsman if a seabird would land on his mast. The group made their way back to Canto Casino and bet a patron that they could cause a bunch of SE-8 server droids to crash together by ordering drinks and then moving while the droids attempted to deliver the orders. This happened outside of Ganzer's Grotto and caused Ganzer to come out and see what 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 with Ganzer about his time spent with the Lucky Three. He shared his theory that a single brother was lucky, while two of the brothers together had terrible luck. When all three brothers were together, everybody in the vicinity 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 accompanied them and continued to make random wagers on the way. This included betting an intoxicated human that he could balance on a planter. By winning this wager, his cache of Cantocoins ended up totaling 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 one of the fathiers named Time for Flatcakes. Sonmi, hungry from not eating all day, absentmindedly commented 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 removed his shoes. He started 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 in the night, none of the entered fathiers were very good. She explained to Sonmi that it was claiming race and any fathier could be bought for 40,000 credits. This prevented owners from running fathiers that out-classed 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, in hopes that their luck would make the longshot pay off.
They went back 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 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.
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