The plot of "There Will Be Blood" follows Daniel Plainview's inexorable rise and moral decay. Initially a lone silver prospector, he discovers oil and adopts H.W., the son of a worker killed in an accident, to craft a relatable "family man" persona for business deals. He is lured to Little Boston, California, by Paul Sunday with the promise of an ocean of oil under his family's ranch. There, he meets Paul's twin brother Eli, a charismatic preacher who becomes his primary antagonist.
A key turning point is an oil derrick explosion that deafens H.W., creating a rift between him and Daniel. Later, a man claiming to be Daniel's half-brother, Henry, arrives, providing Daniel a brief sense of family before he discovers Henry is an impostor and murders him. To secure a pipeline deal, a landowner forces Daniel to be publicly baptized and humiliated by Eli.
The narrative jumps to 1927. Daniel is now an immensely wealthy but alcoholic recluse in a vast mansion. A grown H.W. announces he is moving to Mexico to start his own oil company, leading Daniel to viciously disown him, cruelly revealing his orphan origins. Shortly after, a desperate Eli visits. His investments were wiped out in the market crash, and he offers to sell Daniel the drilling rights to the last remaining oil-rich property. Daniel agrees, but only if Eli denounces his faith and admits God is a superstition. Eli complies, only for Daniel to reveal the devastating truth: he has already drained all the oil from that land years ago via drainage from his surrounding wells, famously taunting him with the line, "I drink your milkshake!" In a final, shocking explosion of rage, Daniel chases Eli around his private bowling alley and bludgeons him to death with a bowling pin. The film ends with Daniel, surrounded by his wealth and the body of his foe, calmly stating, "I'm finished."