While pursuing Jasmine and Glock through the Os-Mine Hills, Lief and Barda stumbled across Fidelis by accident. Since Lief did not have the real Belt of Deltora on him, Fidelis remained asleep as they headed into the underground sea. As Lief passed by his head, Fidelis opened one eye, briefly mesmerising him before closing it again.
When Lief, Barda and Jasmine set out to awaken the seven dragons of Deltora, they travelled to the Os-Mine Hills first, since they already knew Fidelis was there. They were confronted by a group of Granous en route, and Lief attempted to summon the Topaz dragon in desperation. He succeeded, and Fidelis took the opportunity to feed on the Granous. He returned to Lief's group shortly afterward.
When Lief told him about the Four Sisters, the Topaz dragon agreed to help destroy the threat once it had eaten and recovered its strength. However, when Lief mentioned that the Sister of the East, the only one they knew the location of, was in Dragon's Nest, Fidelis abruptly changed his mind. The dragon told Lief that he was not concerned for Ruby territory, and even if he was it would break the promise Fidelis made to Doran if he entered another dragon's land. The Topaz dragon proceeded to explain how the Ak-Baba slaughtered the dragons until only one was left in each tribe, and Doran convinced them to sleep and not to encroach on the other dragons' territories. Fidelis then told Lief that if the Ruby dragon refused to help or they could not find it, he would not help them, but if the Ruby dragon was dead, he may.
Fidelis was not seen in the book again, but it was mentioned that Rolf saw and was frightened by him. The guards accompanying Lief, Barda and Jasmine were concerned about the sounds of the dragon feeding on more Granous, but Barda convinced them that the noises were coming from wolves.
Having regained his strength, Fidelis sensed that the Sister of the South was in Del and began attacking the palace. He was hindered by the people of Del, who rose to defend their home. Nonetheless, he was able to save Lief from the dog and bird faced monster, only to be driven off when Gla-Thon shot him with an arrow. Lief summoned Fidelis when he learned where the Sister was located and the dragon carved a pit into the foundation of the palace to reach it. Again the townspeople attacked, and he was injured by Lindal of Broome, before Barda calmed the crowds. The two-faced monster reappeared however, and, being in close proximity to the Sister, it was able to withstand the dragon's attacks and inflict serious damage. However, Nevets and Steven killed the beast, allowing Fidelis to destroy the Sister.
Later, when Lief, Barda and Jasmine learn of the grey tide, he offered to fly them to the Plains of Hira. He partook in the battle against the Ak-Baba, and destroyed the grey tide along with the other dragons after Lief called them. Afterwards, he returned to Del to drop off the companions before returning to the Os-Mine Hills. He appeared with the rest of the dragons to celebrate Lief and Jasmine's wedding.
Fidelis, like all Topaz dragons, has golden-yellow scales and a pale underside that changes colour to blend in with the skies during flight. He has white claws and teeth, a black, forked tongue, and hypnotic, golden eyes.
Fidelis can breathe golden fire like all Topaz dragons. He has quite some endurance, being able to break through a castle wall while being attacked. Like all dragons, it is assumed that Fidelis most likely has hypnotic eyes and telepathic abilities. He is quite strong, being able to carry Lief, Barda and Jasmine all the way from Del to Hira, as well as being able to fight numerous Ak-Baba and the grey tide. Fidelis, like all dragons, can enter an enchanted sleep, allowing him to sleep for centuries without eating or drinking.