Siren's Song is the 20th episode of Land of the Lost (1991)
In the beginning of the episode, Tom Porter fights with Shung on a beach and calls to his wife Natasha to save herself. Natasha tries to run to safety but runs into Scarface. Before he attacks her, though, Tom wakes up, all this having been a dream. He wakes up on the same beach. Kevin, Stink and Namaki are building a vollyball net, while Annie and Tasha play with a Frisbee. Tasha goes to play with Namaki, but he states he doesn't want to play with a dinosaur ("Thunder lizard").
Tom sits there watching until he sees something strange: His wife walking up on the beach from the ocean. After a second, he realizes it is not his wife. It is Christa. She asks if he is okay, to which he says that she looked like Natasha walking out of the water (Christa thinks he means Tasha the dinosaur, which seems to insult her). He states that Natasha loved the ocean. He starts to apologize about talking about his wife so much, but Christa states that he misses her like she misses her own family. Kevin calls to them to come play, but Christa states she has to go somewhere and won't be back until "Next sun" (Tomorrow). Before they start playing, Kevin notices that the ball is gone (Only to see Tasha about to bury it).
As the gang plays (Annie leaves to get the volleyball that Namaki spiked too far), they hear a strange, creepy music coming from nowhere. After it ends, Tom notices that Annie has not returned. He goes to the place she went to find the volleyball, but only finds the ball, no Annie.
Back with the rest of the gang, Tasha is looking at a pair of footprints in the sand. Kevin has disappeared. He had went to look for Annie by some rocks and disappeared. Suddenly, Tom hears Kevin call to him. He finds Kevin being confronted by a Triceratops. Tom and the rest try to distract it by making loud noise, but Namaki attempts to scare it away by making faces at it. This works. Afterwords, Kevin shows Tom what he found in a bush: Annie's hat.
After searching the beach, they do not find Annie. Namaki carries a sleeping Tasha. When asked why he does not like Tasha, Namaki states that a dinosaur gave him the scar he shows to them. Tom says they will eat, get a good night's sleep, then go and search for Annie tomorrow. Later, Kevin wakes up to find his father standing next to the ocean sad. He continuously blames himself for Annie being lost, but Kevin says that these things cannot be under his control and he shouldn't blame himself. Kevin suddenly gets the idea that Annie's disappearance may have something to do with the music they heard earlier, because Annie disappeared right around the time the music was heard.
Tasha wakes up the next morning and finds Kevin gone again. Tom goes to find him. Kevin goes into a cave to find Annie mesmerized by a strange creature who, when Kevin looks at it, looks exactly like their mother. Annie, believing that this is their real mother, asks if they can "come to her" but the creature asks them to wait for their father.
Tom, Stink, Namaki, and Tasha look for Annie and Kevin. Tasha is upset, but Namaki calms her down. Tom, sitting in sorrow about what is happening, suddenly hears the music and is entriced by it, following it. Stink also hears it, but Namaki and Tasha are unaffected. Namaki and Tasha are unaffected because they cannot hear the music (Tasha cannot hear over the sound of the ocean, and Namaki is listening to Kevin's music player. Namaki gets the idea to have Stink follow the music so they can find the Porters.
In the cave, Tom finds his children and wants to join them and their "mother". He reaches out his hand to take hers, but before he can, a monsterous serpent comes out of a hole and attacks. Tom looks at "Natasha" and sees her turn from the look of Natasha to its true look, realizing she is not Natasha.
Namaki, Tasha and Stink arrive at the cave. Namaki goes in alone to find the Porters. Tom has fallen for the "Natasha's" trick again, but Namaki stops him and tells him he is under a spell. Namaki attempts to fight the serpent. Before it can hurt the Porters, though, "Natasha" throws something at it and it disappears. Tom sends Namaki and the kids out of the cave and asks the crearture that pretended to be Natasha why she brought them there. She states that she was once very pretty, but this became more important to her than her family, so she was sent here with no hope of ever seeing her family again. This drove her to summoning the Porters here. Tom states he was the same way with his job. He always put it first, and he argued with his wife about this the day she died. The creature lets him go.
When he gets outside, Tom thanks Namaki. Annie says she feels bad for the creature in the cave because she is lonely. Kevin deduces that the creature was a Siren. Namaki asks Tom what happened to her now. Just as he says this, a beam of light comes out of the cave ascending to the heavens. The Siren is now free, it seems.