The Forest House is a novel by Marion Zimmer Bradley about Eilan, the granddaughter of a Druid leader in Britain who becomes a priestess and defends her people. After her father takes over from her pacifist grandfather, he begins urging less cooperation with the Roman Empire. Eventually Eilan must sacrifice herself to avoid an uprising and save her son. The book creates a fantastical world centered around antiquity and themes of pacifism, sacrifice and redemption.
In the early days of the conquest, when the Roman Legions are aggressively persecuting the Druids, the sanctuary of the Goddess on the isle of Mona is destroyed and its Druids are murdered and its priestesses are raped. Mona had enjoyed a degree of independence from Roman rule for almost twenty years because Boudica's revolt had forced Roman general Gaius Suetonius Paulinus to withdraw before consolidating his conquest. When the Romans returned under Gnaeus Julius Agricola, they were determined to decisively break the power of the Druids. After the destruction of the sanctuary, the raped priestesses that conceive children kill all of the girl children but leave the boys alive that are born and then kill themselves rather than live with the atrocities done to them; the males later became a rebel group known as the Ravens, which swore vengeance against Rome. Lhiannon, one of the remaining priestesses, re-establishes a new sanctuary at Vernemeton (Most Holy Grove), or The Forest House, which is partially controlled and protected by the Romans.
The novel tells the story of Eilan, granddaughter of the Arch-Druid of Britain. She hears the calling of the Goddess and is chosen to become a priestess at Vernemeton, and later to succeed the dying Lhiannon as High Priestess. However, before her calling, she hears the voice of her heart, and during the magic night of Beltaine, conceives a son with Roman officer Gaius Macellius, son of the high-ranking Camp Prefect at nearby Deva. Gaius is an inheritant of royal blood through his Celtic mother of a southern tribe, the Silures. Eilan knows their son, Gawen, whose bloodline comes from the Dragon (Celtic royalty), the Eagle (Roman Empire), and from the Wise (Druids), will play a crucial role in Britain's future, and makes great sacrifices to protect him in his youth.
A major shift in the balance of power is in the air; Eilan senses that the death of her peace-loving Arch-Druid grandfather will cause it. She tells her friend Caillean (who was rescued from her uncaring mother in Hibernia by Lhiannon) to take a group of young priestesses to the isle of Avalon to found a new sanctuary and become the first high-priestess of Avalon. In Vernemeton, Eilan is increasingly pressured by the new Arch-Druid, her father, to stop promoting peace and collaboration with the Romans. In a dramatic showdown she sacrifices herself (along with her love Gaius) to avoid a bloody insurgency and, in particular, to save the life of her son Gawen.