"Stay there," the woman in the brown leather jacket said to Tilly. She strode across the living room, pulling a glowing ball from her pocket.
"On three?" said the man in the boiler suit.
"Get on the other side of the doorknob first," said the woman. "Let me be the one nearest the opening."
The man shifted over and let the woman take position. They nodded through the count together, then the man opened the door a few centimetres and the woman dropped the glowing ball just outside the door.
The man slammed the door shut. All three of them, the man, the woman, and Tilly, listened to the screams of the hostiles rise to nothingness and the glow fade from under the door. Tilly noticed that the man and the woman seemed to be able to hear the screams for longer than she did.
Tilly started to say something when the hostiles seemed to be well and truly gone, but the man in the boiler suit held up a hand and she stopped. She waited until the man and the woman left the door and sat down when they did.
"How many do you have left?" said the man.
"Seven," said the woman.
"How soon do you think they'll be back?"
The woman frowned and waved her fingers in the air as if tracing the flights of dust motes in the air. Tilly figured this was the Other equivalent of counting on one's fingers.
"In this perception? An hour, maybe longer. It depends on their breeding capabilities."
"So, then... we could leave now and have time to get out of the building," said the man in the boiler suit.
"Wouldn't solve anything," said the woman. "They're still here, and we're still under orders to clean them up."
"What if you didn't?" said Tilly.
"They'd start by either eating or occupying all the lifeforms in this building," said the woman. "Which it seems they've already done with at least one of your neighbours, maybe more."
"Then some of them would spread to adjacent buildings and all the things living outside," said the man. "The ones that stayed here would consume all the carbon in the building, from the houseplants to the plastic shower curtains."
"And so on, until the entire planet is consumed," said the woman.
"Then they consume each other, and then..." said the man. "We haven't been able to track this part of their lifecycle very well, but at some critcial point they build some sort of catapult and launch a cohort of them into space, to find the next target planet. They're sort of like your viruses that way — they just suspend life processes if they get frozen. Are you all right?"
Tilly gave her head a shake and carefully sipped from her cup of rapidly-cooling tea. "Humans aren't like that," she said. "We most definitely don't suspend life processes very well at all. And the only thing that kills them are those ball.... things." She pointed at the woman's pocket.
"Or if we could keep them from carbon for about sixty seconds. Those ones that aren't occupying a host body to feed on — they need to feed constantly."
"You do have an awful lot of carbon on your planet's surface," said the man in the boiler suit.
Tilly frowned and set down her teacup. She blinked. "I have an awful lot of something else in this apartment," she said. She got up and went to the kitchen, returning after a moment with several rolls of tinfoil under her arm.
"Would this help?" she said.
"How much do you have?" said the man in the boiler suit.
"All of this plus about six dozen rolls under the bed."
The woman in the brown leather jacket stood up. "Then we better get going."