SOLVED. Girl works in office. Finds old box of stuff that relates to the owner of the building. Hides it under her desk. She even takes home part of it. [s]

[Sarah]

Maybe it was an artifact office of some type she works in.
I cannot remember the name!

[Winterwhisper]

Could it be The Clockmaker's Daughter by Kate Morton:
In the summer of 1862, a group of young artists led by the passionate and talented Edward Radcliffe descends upon Birchwood Manor on the banks of the Upper Thames. Their plan: to spend a secluded summer month in a haze of inspiration and creativity. But by the time their stay is over, one woman has been shot dead while another has disappeared; a priceless heirloom is missing; and Edward Radcliffe’s life is in ruins.

Over one hundred and fifty years later, Elodie Winslow, a young archivist in London, uncovers a leather satchel containing two seemingly unrelated items: a sepia photograph of an arresting-looking woman in Victorian clothing, and an artist’s sketchbook containing the drawing of a twin-gabled house on the bend of a river.

[Sarah]

That’s it!!! I couldn’t remember! Thanks so much!

[Kris]

Glad you found your book, Sarah. Here's the link for Winterwhisper's find - The Clockmaker's Daughter by Kate Morton.