During the tumultuous English Civil War, an alchemist's assistant named Whitehead finds himself fleeing from the iron grip of the strict Commander Trower. Just when it seems all hope is lost, he is rescued by a rugged soldier named Cutler, who bravely eliminates Trower to ensure Whitehead's escape. Along their journey, they encounter two deserters, the seasoned veteran Jacob and the naïve Friend. The unexpected band of four sets off to locate an ale house that Cutler claims is just around the corner.
However, instead of finding the ale house, Cutler leads them to a strange field abundantly filled with mushrooms. Here, he prepares a meal using these mushrooms and encourages the others to indulge, although Whitehead abstains due to fasting. After their feast, they unearth an Irishman known as the Wizard O'Neill, a character both cunning and dangerous, who is also a rival to Whitehead's master. O'Neill quickly takes charge, revealing he possesses knowledge of a hidden treasure located within the field.
The group soon arrives at O'Neill's camp, where he enforces his will upon Whitehead, coercing him into becoming a human divining rod to locate the treasure. Using Whitehead’s abilities, they discover the treasure is, in fact, nearby the camp. O'Neill orders Jacob and Friend to start digging while he takes a moment to rest. As they dig, Jacob falls under the influence of the hallucinogenic mushrooms, leading to chaos where he attacks Friend. The situation escalates when Cutler interjects with laughter but in a moment of conflict accidentally injures Friend, who dies after delivering a bitter message about hating his wife.
Cutler is left to continue the digging alone while Whitehead, mourning the loss, discreetly hides Friend's body. As tension rises, O'Neill notices the disappearance of Jacob and Whitehead, leading to a frantic chase. After a surreal experience induced by a high dose of mushrooms, Whitehead conjures a storm that wreaks havoc on their camp. Meanwhile, Cutler discovers the so-called treasure is merely a skull and, in frustration, shoots it.
In a climactic turn, Cutler confronts O'Neill, accusing him of deceit. The confrontation ends abruptly when O'Neill retaliates and kills Cutler. In an act of desperation, Whitehead and Jacob gather weapons from Cutler's arsenal to prepare for an assault as Friend returns unexpectedly, revealing their position. A violent skirmish ensues where O'Neill shoots Jacob, but Jacob bravely strikes back, fatally wounding O'Neill. The battle takes a tragic turn as Jacob perishes, acknowledging that the true treasure was the bond they shared.
In a final confrontation, Friend tries to weaponize Cutler's pike against O'Neill but meets a grim fate at O'Neill's hand. Seizing the moment of vulnerability, Whitehead ultimately ends O'Neill’s reign by shooting him from behind.
As the dust settles, Whitehead solemnly buries his fallen comrades in the ground they fought over and finally departs from the field. Dressed in O'Neill's clothes, he gathers his master's stolen documents and retraces his steps to the hedgerow where their venture began, deafened by the echoes of battle around him. Upon stepping through the hedge, he witnesses a poignant vision of friendship—their trio reunited in spirit, standing together once more.
