Ellie Jordan: Ghost Trapper, book 3: The Crawling Darkness
J.L. Bryan2015

Paranormal investigator Ellie Jordan faces a new case in an apartment building where a twisted, dangerous entity emerges from closets and doorways to terrorize the residents at night. A powerful spirit, it feeds on fear and takes the shape of its victims' worst nightmares.

Ellie and her mentor Calvin have tried to capture the same entity before, in a different house nearby, an attempt that ended in disaster. Now, with the help of her apprentice Stacey, Ellie must try again to capture the elusive shapeshifting ghost before it can claim another soul as its own.