The Frozen People (Ali Dawson #1) by Elly Griffiths

Some murders can’t be solved in just one lifetime.

Ali Dawson and her cold case team investigate crimes so old, they’re frozen—or so their inside joke goes. Nobody knows that her team has a secret: they can travel back in time to look for evidence.

The latest assignment sees Ali venture back farther than they have dared before: to 1850s London to clear the name of Cain Templeton, an eccentric patron of the arts. Rumor has it that Cain is part of a sinister group called The Collectors. Ali arrives in the Victorian era to another dead woman at her feet and far too many unanswered questions.

As the clock counts down, Ali becomes more entangled in the mystery, yet danger lurks around every corner. She soon finds herself trapped, unable to make her way back to her beloved son, Finn, who is battling his own accusations in the present day.

Could the two cases be connected? In a race through and against time, Ali must find out before it’s too late.