Well, now! At 850+ lines (depending on translation), Book IV is the longest in The Odyssey, so it might be easy to get a little lost as to what's actually, y'know, happening. Well, here's my gloss--caveat, caveat, caveat.
Lines 1-72: Telemachus and Pisistratus arrive in Sparta in the middle of a large wedding feast for two of Menelaus' children. They are seen by a servant of the king who asks the king if they should be invited to the feast. Menelaus insists that they be brought in, recognizes them as sons of royalty, and seats them beside himself at the feast.
Lines 73-125: Telemachus quietly expresses his wonder at the size and luxury of Menelaus' palace. Menelaus overhears and admits that he has amassed great wealth, but states that he only did so via traveling a great deal after the Trojan War. He laments the many great men lost during that struggle, singling out Odysseus.
Lines 126-134: Telemachus bursts into tears. Menelaus becomes certain that this strange visitor is indeed Odysseus' son, but isn't sure whether to ask him directly.
Lines 135-170: Helen, Queen of Sparta, enters with a large retinue of servants. She immediately recognizes Telemachus as Odysseus' son and Menelaus agrees with her.
Lines 171-239: Pisistratus announces that his companion is, indeed, Telemachus. The entire party begins to weep for what they all lost at Troy before Pisistratus says they shouldn't cry over dinner. Menelaus agrees and says he sees much of his father, Old Nestor, in him.
Lines 240-262: The party returns to feasting, and Helen drugs them all so that they will no longer weep over sad memories.
Lines 263-342: Helen and Menelaus each tell stories of the bravery and cunning of Odysseus before Telemachus suggests they all go to bed and talk of Odysseus in the morning, which they do.
Lines 343-369: Once Dawn arrives (rosy fingers and all), Telemachus tells Menelaus about the suitor situation and asks him for any news of his father.
Lines 370-665: In a long passage, Menelaus tells of the time he was stranded off the coast of Egypt and of his encounter with Proteus, The Old Man of the Sea, who told him not only what he needed to do to get home, but also of the fates of Agamemnon and Odysseus. He then asks Telemachus to stay with him for several days.
Lines 666-702: Telemachus excuses himself from a long stay, citing a need to return to his crew, which he left behind at Pylos. Menelaus sees the wisdom of this and grants Telemachus a present of a very fine mixing bowl forged by Hephaestus.
Lines 703-759: Meanwhile, back in Ithaca, the suitors have discovered that Telemachus has gone to Pylos, perhaps to raise some men against them. They resolve to take some boats and ambush and kill him before he makes it home.
Lines 760-863: Penelope finds out not only that Telemachus is gone but also that the suitors are plotting to kill him from her servant Medon. The old nurse admits to her knowledge of Telemachus' journey and tries to comfort her queen who prays to Athena, who hears her prayer.
Lines 864-883: Some of the suitors mock Penelope's cries to the goddess before they are reprimanded by Antinous. The ambush party leaves shore and waits until nightfall to depart.
Lines 884-end: Penelope is inconsolable until Athena sends her a phantom of her sister to comfort her. Penelope, realizing that the phantom is from the goddess, asks for news of her husband, but Athena refuses to answer. Meanwhile, the suitors set off for their destination and lie in wait for Telemachus.