Aaron Callum

A brown rat working for the Britannia's mail system. Married to Tiffany, and in an open relationship with the same. Father of Rose, adoptive father of Tessa.

Aaron and Tiffany find Tessa as a baby, left in a basket in the Britannia metro with a note that her name is Tessa Edwards and that she is very important. Tiffany quickly falls in love with Tessa and fights tooth and nail to adopt her, renaming her "Angel."

When Julian's team follows Tessa to the post office, Aaron catches them and is angry she wouldn't even say hello to him. He scolds her about checking in on occasion, to Kevin's and Lee's confusion. When Tessa tries to brush him off by informing him about reporting to G deck 5 for assignment, he asks if they will join the family for dinner. Tessa tries to brush it off, but Julian and Lee immediately accept.

The Callums meet up with Julian's team for dinner to celebrate the team's saving the Britannia. Tiffany goes in ahead of them and argues with the host about their reservation, but Tessa is inclined to pretend she doesn't know her. The host finally lets them in, and Tiffany immediately makes a scene about being proud of Tessa.

The restaurant owner Llewellin greets them, and both Rose and Tiffany swoon over him. After they place their orders, Tiffany immediately grills Julian about how long he's been sleeping with Tessa. She points out that they are clearly in love, and she's even a little offended that Tessa is such a prude. Aaron interjects that not everyone can pull off an open relationship. Julian apologises for not telling them sooner, as it's against CORE regulations, but Tiffany assures him that it's fine, they were just hoping Tessa would calm down if she got laid. So Tiffany fans the flames by showing Julian Tessa's baby pictures. (j/k) Tessa is relieved when the starters arrive, until Tiffany hits on the waiter.

After the meal, Llewellin offers to let them leave by the service tunnels to avoid the paparazzi. Aaron and Tiffany leave through the main entrance (with company), as they have no risk of being assaulted by the press, but not before seeing off Tessa and Julian. Aaron then leaves Tiffany with Noah for the weekend.

Aaron calls Tiffany when she is with Noah, concerned that the CORE is taking over the Britannia after Merlin's attack. He wants Tiffany and their daughters off of the ship as soon as possible due to Woodgrove's instability and likelihood of the Anarchists and CORE fighting it out with the Britannia in the middle. He suggests that Tiffany take them to her mother's place, but they would rather endure the space death ray than her mother. Noah overhears their conversation and offers his house in Melbourne.

As Tessa has a few weeks left on her service, Aaron and Tiffany fight for her parole. Meanwhile, they take up Noah on his offer, with Rose joining them after a week and Tessa awaiting the parole results. It is finally granted, to their elation, but Tessa has other ideas and is furious at them, especially after not asking her how she felt, and particularly on the day she was due to go into space. Aaron wants her to stay with them to talk it out, but Tessa refuses, as she is loaded. The last thing she ever says to them is that she doesn't want to see them ever again. In the future (past), their timeline is erased, and her family will never be born.