I picked this up in a charity shop years ago. It’s a novella that is apparently part of a series.
In postwar London, an unexploded bomb goes off when the bomb squad mess up and this frees a population of quasi-human beings who have lived underground. They perpetrate some bizarre murders.
Honoré (who sees people’s past, present and future and whose day job is rendered non-judgementally as “spiv”) and Emily (who has clearly travelled from what is more like our time but has amnesia) are hired by a poet who is convinced these creatures are going to kill him next. And stuff.
I’m still not sure where the time travel really comes in to this story; it would be much better as a creature feature. Not very memorable, it’s going right back to the charity shop.