While A Star Shall Fall, the third book in the Onyx Court series, can be read as a standalone plot-wise, readers will get a lot more out of the characters and the setting by first reading the previous books, Midnight Never Come and In Ashes Lie.

In 1666, the fairies of Onyx Hall saved London from burning to the ground by imprisoning the great Dragon Spirit of Fire. However, the Dragon was so powerful that the fae could not keep it locked up for long - so they sent it to space. The Dragon was stuck on Halley's Comet.

In 1705, Sir Edmund Halley predicted that the comet would return. Since then, Queen Lune and her mortal prince-consorts have tried to find a way to imprison the Dragon again when it returns with the comet. For fifty years the faeries have frantically searched for that way without success. They have also been forced to keep count of the years in a way that is not natural to fairies at all.

In 1757, Queen Lune's current Prince of Stone is young Galen St. Clair, who is trying to find the answer in science. As a member of the Bluestocking Circle, where learned men discuss scientific matters, he hopes  to find someone there who can help the fairies. He has also a way to get into the Royal Society. However, even if he manages to find someone, he will either have to let the man work without knowing what he is really doing, or tell him about the fae Court.

Sprite Irrith returns to Onyx Court after being away for several decades. On the way, she is attacked by a desperate fae who is apparently trying to get to the tithe of bread that Irrith is carrying. Eating the tithe protects the fae from iron and other mortal hazards. Irrith manages to escape and get to the Court where she is welcomed, but she finds out that parts of the Onyx Court are disappearing because mortal London is changing. Many of the fae fear not only the more immediate threat of the returning Dragon, but also of the science that the humans are using more and more. Many are deserting the Court, and soon Irrith, too, must choose where she stands.

The plot centers on investigation - both for a way to trap or defeat the Dragon and Irrith investigating the happenings in the Court. A curious Irrith soon becomes convinced that Lune is hiding something from her subjects. She also finds out that a fae faction called the Sanists are not happy with Lune's leadership and are trying to pressure her to step down. Some also say that the Onyx Court is crumbling because Lune herself is crippled.

Lune relies heavily on her young prince. Galen is doing his best but still unaccustomed to his duties and privileges. He has his own troubles, too. His family is impoverished, and his three sisters need dowries. Because of that, his father is pressuring him to marry a rich woman - and soon. Unfortunately, Galen is in love with Lune and feels that it would be unfair for any woman to marry him is such circumstances. Yet, because of his loyalty to his family, Galen agrees and starts to look for a suitable candidate.

There are two main point-of-view characters: Irrith and Galen with short passages from Lune, mostly when she is remembering the past.

The cast is large and delightful with two main point-of-view characters. Irrith (the first POV) is headstrong and refuses to bow to politics, but also loyal and tries to do the right thing. Galen (the other POV) tries his best to fulfill his duties both in the mortal realm and in the fae Court. Lune is a more distant character this time, the Queen trying to save her city. Many of the minor fae characters from the previous books return, but the humans have, of course, perished.

Two major new fae characters debut: the centaur Kristes, an architect from Greece who is trying to keep the Onyx Court together and is one of Irrith's few friends; and a djinn from Araby joins the Court - Abd al-Rashid, traveler, scholar, and scientist. The reserved fae offers his services to help the Court, but Lune and Galen are wary of trusting him.

The main focus is on science. A scientist even starts to study the Fae realm and find out the natural laws there - why and how fae react physically to iron and church bells, even to the name of God. A few new fae characters build machines, too. Even though the fae do not trust science, their world has some modern touches: they have newspapers and carry guns.

And hanging over it all is the constant threat of the Dragon who might destroy everything. Brennan's pacing is excellent right up to the bittersweet ending.