Held By Magic by LJ Swallow

The London fae court is in turmoil, and demons plan to take control.
I make one tiny mistake, and suddenly I’m marked for death, pursued by a demon prince while fending off my fae ex-lover. Who knew stealing a magic box could cause so much trouble?
I hope the demons don’t overthrow the fae because they’re my best customers—especially the enigmatic and immortal Collector who really shouldn’t be friends with a half-demon thief. I’d like to be more than friends with the too-sexy-for me fae, but he always keeps our relationship strictly professional.
My skills are more in demand than I realise because three hot demons from a mysterious institute track me down.
Powerful but seductive elemental demon Cillian.
Sharp and guarded djinn Morgan.
And their companion Dex who’s definitely not human and strangely familiar.
Hook ups aren’t on my agenda, but these guys have some interesting skills to distract me from my imminent death.
The trio and their institute ask me to locate more of the mysterious boxes, and in return they promise to cure my mark and keep me alive. Simple. The problem is, these boxes are mixed up with the demon and fae troubles, and now so are we.