When Heracles was near his death (the subject of another play by Sophocles - The Trachiniae), he wished to be burned on a funeral pyre while still alive. No one but Philoctetes would light the fire, and in return for this favor Heracles gives him his bow. Philoctetes leaves with the others to participate in the Trojan War, but gets bitten on the foot by a snake when walking on Chryse, a sacred ground. The bite leaves him in constant agony, and emits a horrible smell. For this he is left by Odysseus on the desert island Lemnos.
Ten years pass, and the Greeks capture the Trojan seer Helenus, son of Priam. He foretells that they will need Philoctetes and the bow of Heracles in order to win the war. Odysseus sails back to Lemnos with Neoptolemus (son of Achilles) in order to get Philoctetes. The task will not be easy, as Philoctetes bitterly hates Odysseus and the Greeks for leaving him there.