Surprisingly good.

Invisible was published 2014.

A sequel — Unsolved — published 2019.

Emmy Dockery is an FBI research analyst on leave.

She has been obsessed with a large number of fires in which a single person always died, including one involving her sister.

Local authorities, finding no foul play, ruled all these fires were accidental. …

… a preliminary investigation is launched by the FBI …

The New York Journal of Books provided a positive review, saying, “Invisible is a difficult book to read because of the sheer horror and mayhem, but it’s even tougher to put down.”

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Unsolved, the sequel, is equally good.

Twists and turns.

The weird and impossible relationship between Emmy and her ex-fiancé Books continues. Somehow.