Glow ended with Kieran's worrying leadership methods and Waverly's realisation that they have nothing in common anymore. Spark begins a month after and follows Waverly, Kieran and the rest of the children aboard the Empyrean as they race to catch up their sister-ship New Horizons and rescue their captive parents. The book explores the mental strain the kids are under, having to run a ship all alone and the aftermath of Waverly's daring rescue of the girls from New Horizons in the last book.Like Glow, Spark is told from the view points of Kieran and Waverly, but added into the mix are chapters from Seth's point of view. This gives the book balance and allows the author to explore each character's motivations - after the events of Glow I was firmly on Team Seth and dying to get to know Seth better and this style made that possible. Unfairly locked up without a trial, Seth is suffering, and has had the time to recognise that his actions in Glow were symptoms of fear and grief, brought on by the death of his father. Seth displays astounding character development throughout the book, and finds an ally in Waverly, which I enjoyed!Kieran gets increasingly paranoid and power-hungry the longer he acts as Captain, and although I understood his desire to rescue his parents and keep the children in his charge safe, he began to ignore the sound advice of his fellows and punish people for disagreeing with him, which made me very angry. I liked how Waverly stood up to him, but she shouldn't have had to. Waverly is dealing with the repercussions of failing to rescue the adults from their captivity aboard New Horizons - the younger children assume she is cowardly or weak, which is extremely unfair and I loved it when she finally stood up for herself.The plot and pacing of the novel is perfect, the unpredictable twists and turns in the book are engaging and had me on the edge of my seat. Ryan's writing has tightened and matured and this book has better flow than the previous one. liked that the set-backs the kids on the Empyrean face in the book: they didn't accomplish amazing feats that are impossible for a group of children under eighteen. For example, lacking an adult with proper medial training, the kids were forced to learn a lot about taking care of one another, but they never knew or did things that seemed implausible to me. Spark ends with lots of questions still to be answered, hopefully in the next book, and I am looking forward to it!Spark is an impressive followup to Glow, with all the drama and adventure I was expecting. I recommend the Sky Chasers series to those who enjoy a bit of light Science Fiction, and think it's perfect for those who aren't sure if they will enjoy the genre but would like to give it a try.You can read more of my reviews at Speculating on SpecFic.