Princess Cecilia, often called Celie, is the eleven-year-old youngest child of the royal family of Sleyne. She shares a profound emotional connection with Castle Glower, treating the sentient building as a close friend. She spends her time memorizing the ever-changing floorplan and compiling a massive atlas of its rooms.

Prince Rolf is the fourteen-year-old crown prince of Sleyne. Despite his young age, Castle Glower has chosen him as the heir to the throne over his older brother. When crisis strikes the kingdom, he faces intense pressure from the Royal Council, requiring him to employ careful political strategy rather than outright defiance.

Princess Delilah, known as Lilah, is the older sister to Cecilia and Rolf. While occasionally bossy and prone to complaining, she is fiercely devoted to her siblings. She helps coordinate their covert efforts to maintain control of the castle and watches out for her younger siblings' welfare.

Castle Glower is the sentient, magical palace that serves as the seat of the kingdom of Sleyne. It has the ability to change its physical layout at will, adding or hiding rooms based on its moods and needs. The castle acts as a protective force for those it favors and actively inconveniences those it dislikes.

Prince Khelsh is the second son of the king of Vhervhine, a notoriously warlike nation. Banished from his own home, he comes to Sleyne with a large entourage and dark intentions. He attempts to manipulate the kingdom's political instability to seize power for himself.

The Emissary is a leading member of the Royal Council, a group of older men who advise the crown. He seeks to exploit the king's absence by establishing a regency to control the young Prince Rolf, forming an opportunistic alliance with foreign powers to consolidate his own influence.

King Glower is the just and respected ruler of Sleyne. He relies heavily on the wisdom of Castle Glower, consulting it on major decisions including the line of succession. His sudden disappearance leaves the kingdom completely vulnerable to political manipulation.

Queen Celina is the mother of the four royal children and the daughter of a Royal Wizard. She is highly dedicated to the welfare of her family and the kingdom of Sleyne. She disappears alongside her husband early in the narrative after a bandit attack on their carriage.

Prince Bran is the eldest of the royal children. Because Castle Glower determined he would make a better wizard than a monarch, he studies magic far from home rather than preparing to inherit the throne.

Pogue is the son of the village blacksmith and is widely considered the most handsome young man in Glower Valley. Despite his tendency to get into fights, he is fiercely loyal to the royal family and risks his own safety to seek answers about the missing king and queen.

Prince Lulath is the third son of the king of Grath. He initially appears to be a ridiculous and overly fashion-conscious figure who dotes on his numerous pet dogs. However, his opulent treatment by Castle Glower suggests there is more substance to his character than his foppish exterior implies.

Lord Sefton is a member of the Royal Council who retains his integrity during the kingdom's political turmoil. Unlike his corrupt peers, he opposes treasonous plots and possesses some rudimentary wizard training that proves valuable.

Lord Feen is an elderly and somewhat feeble member of the Royal Council. Due to his advanced age and frailty, he is generally unable to meaningfully protest or prevent the more ambitious and corrupt actions of his fellow councilors.

Sergeant Avery is an officer in the royal guard of Sleyne. He leads the search parties looking for the missing king, queen, and eldest prince, and is responsible for assigning bodyguards to the royal children when tensions rise within the castle walls.