We are used to thinking of a politically organized world.  That is,
a country is very likely to butt against another country with a rather
similar state of political organization, and even a comparable amount of
international military, political and economic power.  This was not always
the case.  In ancient times, there were a few well organized countries, and
large areas of the world where kings ruled tiny kingdoms, with complete
local sovereignty but a very limited sway; one could walk across the 
kingdom in a few hours and find oneself in the next.  In a very real 
sense, the "colonial" movements of the eighteenth and nineteenth centuries
were the politically organized governments taking over the last remnants
of the unorganized world.

At the time of the Trojan war, the well organized countries were the
Hittite empire and the double kingdom of Egypt.  These areas were the 
size of modern countries, with large government organizations, standing
armies, and a literate bureaucracy.  The rulers of these states wrote to
each other, addressing each other as "Great King", as distinct from,
as they saw it, the petty kings at large in the rest of the world.  
Just how trivial these petty sovereigns could be is illustrated by the 
Cuchulain saga (a few centuries later, but never mind), which recounts a 
battle in which 300 kings were killed.  And there were presumably survivors.  
And these were all native Irish kings; they didn't have to import a bunch 
of foreign kings to make up the number.

Which doesn't mean that the petty kings couldn't get together and take 
some sort of concerted action.  They could and did.  But the leader of 
such a league was strictly an ad hoc proposition, based on the charisma
or military power of the individual in question.  These leaders had 
titles like "Great King" (David of Israel was so called), "King of kings" 
(or "Shah an Shah", as Mr. Pahlevi was called), or "Wide ruler" (as
Alfred the great, King of Wessex).  There is a fascinating note in the
imperial archives of the Hittites, which might be a query as to whether
somebody who just might be Agamemnon of the Achaeans should be addressed
as Great King, or just as king.

In any event the Achaean Greeks combined together to make war on
the city they called Illios, in the region called Troy.  The reason why
they went to war is lost in the mists of history.  The abduction of 
Helen and "the face that launched a thousand ships" is surely romantic
twaddle made up of whole cloth in the half a millennium between the time
of the war and the time the tale was first written down.  For the Achaeans
had writing, but the art was lost for several centuries until the classical
age of Greece.  (I find it amazing that such a valuable gift could be 
rather casually mislaid.)

In the course of these centuries, the story of the Trojan War grew
in the telling.  It has been suggested that the only part of Homer that
actually dates back to a date near the war itself is the Catalog of Ships
from the Iliad.  The rest of the epic was filtered through the eyes and
mind of various retellers of the story in the intervening ages.

Not only was the real cause of the war forgotten, but the war itself was 
converted from a straightforward conflict to a story of a battle between 
the gods themselves, with their human partisans losing or gaining, 
depending on the alliances and maneuvers of their patron gods.

It is far from clear whether the whole tradition of the war was transmitted 
in the two great epics of the Iliad and the Odyssey, or whether there 
was a residual set of legends articulated by the Greek classical authors, 
who might also have made the things up in the general style of Homer.

Anyway, Neptune was on the side of Troy, and was very unhappy when
the other gods prevailed, and took his revenge as the sackers of Ilium
took to the seas to return home after their victory.  The Odyssey is the 
story of the travail he inflicted on Odysseus, king of Ithaca.  

Agamemnon, when he finally got home, found an unhappy queen who had taken 
a lover, who on the day of his arrival, slew him in his bath.  This placed 
his children, Orestes and Electra, in an impossible position.  They could 
not let the death of their father go unavenged, but when they in turn
slew Clytemnestra and her lover, the gods set the Furies to hound them
for murdering their mother.  Orestes is eventually tried by the demos
of Athens, who permitted him to live.

Another king, in a later story, was Idomeneus, king of Crete, whose 
story provided the basis of the libretto for "Idomeneo".

All this has nothing to do with the opera; I just thought it was fun.
However petty the kings were in actuality, Mozart took them seriously.

Idomeneo's ship is approaching Crete, after years of journey under the
harassment of Neptune.  His son, Idomante, is anxiously waiting him,
and when he hears his father is approaching, he proclaims a feast, and,
in celebration, frees the Trojan captives.  (Nobody explains how the 
Trojan captives arrived, and languished for years in captivity, when
the king couldn't make it home at all.)  He has fallen in love with one
of the captives, Ilia, and says he will marry her when his father 
arrives.  Electra, daughter of Agamemnon, is staying at the court of
Crete (again, nobody explains why).  A strong anti-Trojan, she thinks
it unpatriotic for Idomante to marry one, and thinks that herself marrying 
Idomante would be a good way to get back into the queen business, given 
that the Furies had made her rather unwelcome back in Mycenae.

With Idomeneo's ship in sight, Neptune blows up a storm, and the ship
founders at the last moment.  But Idomeneo manages to ride the wreckage 
to shore, by making a terrible bargain with Neptune; that when he lands 
on Crete, the first person he sees, he will sacrifice to the god.  And 
of course, that first person is his anxious son, Idomante.

Delaying the payment to the god, Idomeneo suddenly notices Electra, and 
quickly realizes she is in the wrong play, and assigns Idomante to take 
her back to the Orestiad, figuring he will be safer there than home in Crete.  
(Electra is very happy to get him alone, away from Ilia, for a few weeks.)
But to leave Crete means taking ship, and Neptune is not so pleased to have
his sacrifice run away.  An awful storm stops the ship from leaving, and 
a horrible monster comes out of the sea and begins to ravage the
countryside.  (In a stroke of genius, the Santa Fe Opera represented the 
monster as the bull symbol so often seen in artifacts of Minoan Crete.)

Idomeneo offers to Neptune to take his own life in place of Idomante.  In
the mean time, Idomante, in a burst of feelings of civic responsibility,
goes off to hunt the monster, to either kill or be killed, much expecting
the latter.  In an amazing turnaround, however, he kills the monster, and
shows up at the temple of Neptune where he proposes to take Ilia as his
wife.  The God himself then speaks, saying he can't bear to be mean to 
young lovers, and deposes Idomeneo as the only punishment for not keeping
his promise, and makes Idomante king (and Ilia queen) in his place.

The happy ending was tacked on by Mozart.  The original story was an 
unrelieved tragedy, in which the god demands the father sacrifice his
child, as in Iphigenia and Agamemnon.  (Perhaps Mozart is emulating the
story of Abraham and Isaac.)  But Mozart doesn't have a tragical bone 
in his body, and can only just barely keep serious for the supenseful 
parts of the opera.  He was clearly just playing at the "opera seria" mode, 
trying it on to see if it suited.  But his light mood is one of Mozart's 
greatest assets.  You are never overwhelmed by Mozart, never want to 
escape him, as I sometimes want to escape Puccini ("Butterfly" is just 
too depressing).  But his main asset is that the man seems incapable of 
putting a note on paper that you don't enjoy listening to.

As usual for the Santa Fe Opera, the staging was very well done.  The 
opera was played on a large stony disk, which in turn represented the 
palace courtyard, the dock where Idomante was to take ship, and the 
courtyard of the temple of Neptune.  Behind the disk, doors opened to 
reveal a back-projection screen, which showed, as appropriate, the throne 
room, the bay where Idomeneo's ship foundered, the ship Idomante was to take, 
the beast from the sea, and finally the altar in the temple of Neptune.  
Closing the doors to change the scene lends it an air of far greater realism 
than the usual slide show.