Summarize chapters 8–13 of The Eagle of the Ninth.

The Eagle of the Ninth, a historical epic by English novelist Rosemary Sutcliff, centers on a Roman Centurion guard named Marcus Flavius Aquila and his travels through Britain in the second century AD. Along with the help of his trusted companion, a Brit named Esca, he steals back an eagle totem from a barbarian tribe, which he believes belonged to his father's legion, and is chased by the hostile horde as he attempts to make it back to safety.
Chapter 8, "The Healer with the Knife": This chapter centers on Marcus's relationship with his uncle and his early interest in the neighbor's young niece, Cottia. The uncle is concerned about Marcus's leg not healing properly—a suspicion that's confirmed when the uncle's surgeon friend inspects the wound—and Marcus pleads with his uncle to be kinder to the neighbors so that he can court Cottia.
Chapter 9, "Tribune Placidus": Marcus's leg finally heals with full functionality even though its scarred and deformed. Marcus releases the wolf he had cared for into the wild and considers future employment opportunities, including work as a secretary to a wealthy man. The uncle has a former friend from the legion over for dinner.
Chapter 10, "Marching Orders": The uncle's friend talks about the mysterious disappearance of the unlucky ninth legion, where Marcus's father was a commander. This is where Marcus first learns that a northern barbarian tribe had allegedly ambushed the legion and taken a precious eagle totem from them, which they keep as protection against the Romans. Marcus opines about the benefits of finding the eagle.
Chapter 11, "Across the Frontier": At the beginning of summer, Marcus and Esca pass through the gate at Hadrian's Wall with Marcus in disguise as an oculist using props provided by the uncle's doctor friend. They build an altar in order to sacrifice an olive-wood bird that Marcus has had since he was a child.
Chapter 12, "The Whistler in the Dawn": Throughout the summer, Marcus and Esca travel around the north part of Valentia but have no luck finding clues of the ninth legion's whereabouts. They turn and head south, where they eventually encounter a man named Guern of the Painted People leading a pony and singing a marching tune that the legions were known to sing.
Chapter 13, "The Lost Legion": Guern invites Marcus and Esca back home with him, and it is there that Marcus sees evidence that Guern was once a centurion. Guern tells Marcus the story of what happened to the ninth legion—they were hammered by numerous attacks that forced them to retreat, but not before suffering great losses. Marcus's father fled and was chased down. Guern saw the barbarian tribe take the eagle totem, and now Marcus decides he must find it to bring peace back to the land.