Belladonna. Poison Garden, #0

Belladonna is the short story prequel to Poison Garden, an urban fantasy series featuring Eliza Moore, a private investigator who can talk to the dead. Eliza "Eli" Moore is the scion of the famed Moore line of seers, and she wishes everyone would stop talking about that. She just opened her own detective firm, and wants nothing more than to live a nice, quiet, non-magical life. Then her first case falls into her lap, and it's a doozy: someone is using belladonna to murder the residents of a nearby assisted living facility.
As a seer, Eli is familiar with poisons; in fact, she still tends her grandmother's poison garden. Knowing how deadly belladonna can be, Eli takes on what she hopes will be her last supernatural case.