Place: India
Time: Late nineteenth century, during the British Raj.

Act 1
The Hindus go to perform their rites in a sacred Brahmin temple under the high priest, Nilakantha. Nilakantha's daughter Lakmé (which derives from the Sanskrit Lakshmi), and her servant Mallika, are left behind and go down to the river to gather flowers where they sing together the Flower Duet. As they approach the water at the river bank, Lakmé removes her jewellery and places it on a bench. Two British officers, Frederic and Gérald (Delibes uses Frenchified versions of the then common English names Frederick and Gerald), arrive nearby on a picnic with two British girls and their governess. The British girls see the jewellery and, impressed with it, request sketches of it; Gérald volunteers to stay and make sketches of the jewellery. He spots Lakmé and Mallika returning and hides. Mallika leaves Lakmé for a while; while alone Lakmé sees Gérald and, frightened by the foreigner's incursion, cries out for help. However, simultaneously, she is also intrigued by him and so she sends away those who had responded to her call for help when they come to her aid. Lakmé and Gérald begin to fall in love with each other. Nilakantha returns and learns of the British officer's trespassing, vowing revenge on him for what he assumes to be an affront to Lakmé's honour.

Act 2
At a busy bazaar, Nilakantha forces Lakmé to sing (the Bell Song) in order to lure the trespasser into identifying himself. When Gérald steps forward, Lakmé faints, thus giving him away. Nilakantha stabs Gérald, wounding him. Lakmé takes Gérald to a secret hideout in the forest, where she lovingly nurses him back to health.

Act 3
While Lakmé fetches sacred water that will confirm the vows of the lovers, Fréderic, Gérald's fellow British officer, appears before Gérald and reminds him of his military duty to his regiment. Gérald sadly accepts that his colleague is correct. After Lakmé returns, she senses the change in Gérald and realises that she has lost him. She dies with honour, rather than live with dishonour, killing herself by eating the poisonous datura leaf.