Doctor Who: The Infinite Quest, on BBC One
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This flash-animated serial aired in 13 installments between April and June 2007, as segments on the children's show "Totally Doctor Who" (which I've never seen). It takes place somewhere within the time frame of the real Doctor Who's third series. While the Doctor and Martha Jones are both voiced by the actors from that show, I tend to doubt that this microseries is canonical. Anyway, I didn't see it until 2019, on a DVD set of several animated Doctor Who adventures.
The story begins with the Doctor and Martha stopping an alien named Baltazar (Anthony Head) from carrying out a horrific plan for the people of Earth, which I don't even want to get into (because it's not really important, anyway). After Baltazar's spaceship is destroyed, he is carried away by a metallic bird named Caw. And of course, Baltazar promises to get revenge against the Doctor someday. Sometime later, the Doctor and Martha meet Caw on his home planet, and he gives them a data chip, one of four that must be found in order to learn the location of an ancient legendary spaceship called The Infinite, which can grant people their heart's desire. Caw tells them that Baltazar has a copy of the first data chip, so the Doctor and Martha will have to find the other three chips before he does, because... Baltazar is really not the kind of person you want obtaining that kind of power. Well... they have a series of weird adventures, trying to obtain the chips, and eventually facing Baltazar once again, when they finally reach The Infinite. Beyond that, I don't want to spoil any specific details of the story, but it was certainly... interesting.