In Book One of "The Odyssey," Athena tells Telemachus to go on a voyage to find his father. Later in Book 16, Athena tells Telemachus that he needs to return to Ithaca to prevent suitors from winning his mother's hand in marriage.
At the beginning of "The Odyssey," Odysseus has been absent for 20 years. Athena tells his son, Telemachus, that he must go and find him, but she does not tell him his location. She does this to send him on a voyage of discovery, which helps him mature and prepare for a leadership role.
Later in Book 16, Athena finds Telemachus in Sparta and tells him he must return to Ithaca to prevent suitors from marrying his mother. She tells him that they have arranged an ambush and gives him instructions on how to prevent it. Athena also tells him that he must first visit Eumaeus, the head of the swineherd, so that he can pass along news of his safe return to Penelope.
After returning to Ithaca and following Athena's instructions, Telemachus finds his father in a hut in the form of an old man. At this point, Athena appears and calls Odysseus outside, which causes his disguise to disappear. Reunited, Telemachus and Odysseus determine a way to overthrow his mother's suitors.