Two years like this, in their company, maybe the hierarchy is a little rusty, they need reminding now that there's an emergency. Maybe she hits it a little too hard, trying to get the balance right: Between leader and friend, crew and family, mother and Captain. Maybe she fell in love with Ed, a little bit, and has only just remembered how dangerous that is. For him, for her. Too human.
Or maybe she's on Bad Wolf Bay, watching Rose run to the wilder twin. Maybe she's in Chiswick, watching Donna roll her eyes and turn back to the phone, feeling one heart breaking right after the other. Maybe letting insubordination rule in those two years of safety and warmth felt better than this; maybe she's wishing she could pull them all into a cabinet behind her, forever. Maybe she's reminding herself that starlight in your soul means loneliness with every sunrise, and all of this was only play. Or a wonderful dream. Or maybe she's just terrified. Another crewman finally locates Andy in the gardens, dripping with such water, arms limply thrown out, dripping down. He shakes and stares.
The solar flares mean Yuri has to watch a repeat message from his brother, who's telling a hilarious story about his husband's spending habits that I guess you have to be Russian to fully understand why it's funny, and in order to make the story even more boring he shows Maggie a map of Earth and where Dagestan lies, on the Caspian Sea. But she's already dead.
"By the sea," it says, and Yuri says it's more like a lake. "Earth is so much water," it says lustily. Yuri yearns for home. "It has so much beauty. We should like that world," it grunts, strangely, and Yuri turns. Her pupils are still normal, but her teeth are scary and she's vomiting great gouts of water through a cruel smile. Sickbay has a situation, he explains on comms, and says it's like she's drowning. Adelaide tries to collect her lost crewman so they can bounce, but he's already dead.
He kneels at the foot of Andy, shivering and shaking; they are both bathed in water. The Doctor begs Andy to stop, promising he can help. They break the tableau, the Doctor and the Captain, but only long enough to get a good look at the men, who are both now dead. They stare and drip; the Doctor and Adelaide run. The things give chase, and it takes a really long time. They lock the doors behind them, just barely a hair's breadth to safety, and the things shoot water out of their hands somehow, great deluges like firehoses. One of them stares at them through the door, and then begins to examine the seals around the door. The Doctor speaks portentously about how water is the most powerful thing. Essentially, it's like time: It keeps rushing, on and on, wearing you down, wearing anything down. Water waits.