Guardian

Agent Kirsten Wren thought she'd seen the true face of evil on the Moon, but the demon Avarazel didn't prepare her for an even more insidious enemy―politics.
After a month to recover, Kirsten returns to active duty with a heavy heart, already missing having all day to spend with her adopted son. Reeling from her disastrous last attempt at a relationship, she takes things slow with Sam, unsure if she's even capable of welcoming a man into her life.
The influential Senator Preston Winchester catches her off guard, requesting her by name to dispel a haunting at his earthbound vacation home. A subsequent string of escalating spectral assaults on seemingly random, unrelated people strikes her as too coincidental, and when the angry spirit attacks her son, Kirsten suspects she is the spirit's true target.
Her investigation leads her to doubt Winchester is as squeaky clean as he appears. She is determined to bring him down, but following her moral compass threatens her guardianship of Evan, as well as the very existence of Division 0.