The Darkness Below

Dr. Harriet Marks has advised the British security services on science for too long, when even gathering forensic evidence at a remote science-terrorist safehouse arouses little professional excitement.
But as a snowstorm closes in, her team realise they're not alone. While some dangers might have once been human, there's also a darkness below that's less recognisable.
A darkness as potentially dangerous as the one already within her.

A speculative novella.