Andromeda was the daughter of a king, but she was not spoiled at all. Andromeda was as kind as she was beautiful. She was even more beautiful than her mother, the lovely Cassiopeia. Andromeda lived in a city by the sea. She was very happy. Everything was going along swimmingly until one day Andromeda's mother went too far with her boasting.
Her mother boasted about Andromeda all the time. Her mother insisted she was the most beautiful child ever born, except for Aphrodite, of course. One day, she boasted that Andromeda was more beautiful than any of the gods' daughters (except for Aphrodite, of course.)
The trouble started when someone told the Nereids what she had boasted. The Nereids were the daughters of the sea god, Poseidon. Poseidon told his daughters all the time that they were more beautiful than seashells. Who could possibly be more beautiful than seashells? (Except perhaps for Aphrodite.) They whined to their father about it, and whined and whined until Poseidon, in a fit of rage, flooded the city by the sea, and sent a huge sea serpent to devour the entire population, thinking that would certainly shut his daughters up.
The people were terrified. The flood had caused great discomfort. Even after the flood waters receded, the monster kept nipping at people. You never knew when he was going to pop up. He had not eaten anyone yet, but he kept trying. The people were very unhappy.
The king asked a local oracle what he could do to put a stop to things. The oracle told him he had to sacrifice his beloved daughter, Andromeda, if he wanted to save his city. It saddened him greatly, but the king ordered his daughter to be chained to a tree on a cliff that overlooked the sea.
That day, the hero Perseus was out adventuring. He sailed past just as the king's servants were chaining the terrified Andromeda to a tree at the edge of a cliff. Perseus fell in love immediately. As soon as the servants left, Perseus rescued Andromeda, using his magic sickle to cut the chains.
Just then, the giant sea serpent reared its ugly head and reached for Andromeda. Andromeda screamed. Perseus, who was still holding his magic sickle, chopped off the serpent's head.
Naturally, after that, Andromeda loved Perseus as much as he loved her. Perseus wanted her to sail away with him immediately. But Andromeda was insistent that he first ask her father's permission to marry him. She would not feel right about marrying anyone without it.
Perseus offered the king a deal. If the king would let him marry his daughter, Perseus promised to chop off the sea monster's head. The king thought it a very good joke when he heard that Perseus had already killed the monster. When he heard that Perseus' mother was a princess in the famous and rich city-state of Argos, he was even more pleased. When he heard that Perseus' was half god, and his father was the mighty Zeus, the king of all the gods, the king gladly agreed to the wedding.
After the wedding festivities, Perseus sailed away with Andromeda. They headed for his home in the city-state of Argos, where they lived happily ever after.
Since Andromeda had left town, and her mother was no longer allowed to boast about her daughter's beauty by order of the king, Poseidon did not send another sea serpent to devour the people, feeling they had learned their lesson. His daughters wanted him to at least go after Andromeda, but Poseidon stood firm.
To be fair, his decision probably had nothing to do with the fact that the ancient city-state of Argos had a nearby harbor for trade and commerce, but Argos itself was located on a plain. Poseidon, god of the sea, could have sent a tidal wave, I suppose, but it would have been a great deal of work, and frankly, he had better things to do.