Huh. Victoria is talking about how stressful the Doctor’s constant adventures are. Is this her last story? Seems to fit since the first of these animated serials I watched was her first.
So, aside from Robson, everyone in the refinery seems to understand there is something in the vents. Harris returned there after he was sure his wife was OK. The Doctor, Jamie, and Victoria all quickly realized that, despite the fact they are supposed to be someone’s prisoners, they are all free to do their own thing. The Doctor theorized that the seaweed is alive…well, he says everything in the ocean is alive to the general disbelief of Jamie. This stuff may be sentient, and it gives off that toxic gas. Since Harris returned to the compound with the promise to send medics for his wife, the Doctor figures Maggie will be OK sleeping off whatever happened, so he and his companions can go run tests on the seaweed back in the TARDIS.
Yeah, there’s more seaweed growing out of Maggie from the looks of things.
By the by, it is a little odd seeing Jamie of all people using the microscope and finding something, but it seems more like dumb luck since Jamie isn’t supposed to be very bright. The Doctor and Victoria find old evidence that the seaweed may have attacked ships in centuries past as some kind of sea monster. Oh, and then the sample they had started to get loose, giving off more gas, terrifying Victoria…but then it retreated and the Doctor was able to secure the case.
Likewise, when seaweed attacks Robson while he tries to take a nap…uh, it doesn’t seem to retreat right away. He does. Harris spotted something, but then it disappeared. That puts the compound on high alert.
Meanwhile, the Doctor and friends go back to Harris’s house only to find more foam and seaweed all over the place. Sure, it seems to retreat from Victoria, but Jamie almost gets pulled under. No sign of Maggie there, but the Doctor figures her husband sent her to the medics. He then goes to the refinery to tell everyone what’s going on, and there he learns…um, Harris never sent the doctors to Maggie. And since this is seaweed, it can be anywhere in the vents.
Or, it could be controlling Maggie and Robson and turning them into seaweed zombies. Robson is going to do something on land. Maggie just walked out into the ocean.