They, along with a whole pack of Diictodons, came through an anomaly from their home era of the Permian to West London Hospital in 2009. One was in the ceiling when it fell through and was caught by Connor and Captain Becker inside a laundry basket. The other was lured by the distress call of another and attempted to get through the anomaly, but it closed and was captured inside Nick Cutter's jacket. Abby and Connor decided to adopt the pair, and were secured in Cutter's car before they were later moved to Abby's flat, and were later named Sid and Nancy.
When Connor learned Abby's brother Jack Maitland was going to be staying and that he needed to move out, he called out to the two Diictodons, as they were going to go with him at a place he could stay in the meantime.
Episode 3.5EditConnor was forced to live inside the ARC, and Sid and Nancy lived in there too. Sid escaped from his cage while Connor was asleep, and ran rampage around the ARC, eluding capture from Connor when he discovered Sid was missing. At some point Sid chewed through some wires of the Anomaly Detection Device and prevented an anomaly from being detected, and James Lester was furious Connor was keeping an animal in the ARC. Sid later showed up in the air vent of a room where a Future Fungus had been supposedly incinerated, and when Connor attempted to recapture him he accidentally restarted the spore's spreading. After the fungus was frozen, Sid was recaptured and left inside his cage with Nancy.
Connor was invited to move into Lester's flat after he ws discovered to be living in the ARC, until he could find somewhere else to go, and Sid and Nancy went with him. They became a constant source of grief for Lester, and when he and Connor went to the ARC one morning, one of the two snuck into the boot of Lester's car and began tearing up some of the classified files kept in there, something Lester was furious to learn when he opened the boot.
Nancy later also ate Lester's exclusive invitation to a dinner with the Chinese ambassador, and started chewing up his jacket. Connor tried to stop her and cover it up, but Lester found out and took the ruined clothing off of her and furiously scared her off with a snarl.
Abby showed up at Lester's apartment one morning, bringing Rex with her because she claimed he was lonely and missed the two trouble-makers. As they curiously examined each other, Abby invited Connor, Sid and Nancy back to the flat because Jack had left, and Connor was relieved as he ws worried the two Diictodons' lives were in danger with Lester around.
Sid and Nancy re - appear in Primeval Revived.