As with most trilogy enders, Crown of Fire is a letdown. I'm not even so sure if Fusion Fire needed to be continued.
The plot follows Brennan and Firebird as they planet-hop, fighting and escaping the forces of Three-Zed while their twin boys are being kept on the other side of the Whorl. Meanwhile, a young Shuhr woman has been impregnated with a zygote of Brennan, without his knowing.
Firebird is charged to where the crown of her people for a night to see who his really trying to attack them. That's where the title comes from.
The villain is a typical serial killer character disguised as someone really interesting. Like I've said before, the Firebird trilogy is a deception; typical plot points disguised as something original.
The plot kind of meanders along with action interruptions. At least the characters are consistently perfect. Her characters actually come off as boring and un-lifelike.
There are also too many near-death escapades that leaves the heroes, primarily Brennan, alive. I can't believe he almost died twice. Both times he was miraculously healed. First, he almost died by the serial killer, and second he almost died in a space battle.
The end was a letdown because Tyers set up a really good ending that she didn't do. I've never really liked series enders, and this one is no exception. But what can I expect from a debut trilogy? I've given her a chance with this series, but she needs to improve with her next book. Combining her original ideas with original plots would make her better than she is now.