If you read the next books in the series you will discover that there is lots of trouble on the horizon. There is the battle of the labyrinth (maybe i cant remember if it was this book the letter was sent in ;)) also their is the Titan war. Poseidon cannot directly interfere with his sons affairs so he has to do it in subtle ways. This letter is telling Percy something bad is coming without telling him the problem or the solution. It is indirect so Poseidon is allowed to do it.
Hope it helped :)
The cast of Brace Yourself - 2001 includes: Patrick Cavanaugh as Charlie Kristen McCullough as Sarah
Julia Brace died in 1884.
Wilma Rudolph's brace was on her left leg.
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Wolfgang Amadeus Mozart - O Fortuna
Brace (as in, "brace yourself").
Brace Yourself for the Mediocre was created on 2004-10-19.
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The cast of Brace Yourself - 2003 includes: Adz Hunter as Manuel
The cast of Brace Yourself - 2013 includes: Carys Watford as Clara
Brace Yourself Bridget is an Irish band based out of Cleveland, OH. Brace Yourself Bridget was a phrase used by an Irish comedian many years ago to describe foreplay in many an Irish marriage. The husband would get into bed and say to the wife "Brace yourself Bridget!"
brace yourself
Brace Yourself - Dropping Daylight album - was created on 2006-04-11.
The cast of Brace Yourself Sydney - 1993 includes: Julian Clary as himself
The cast of Brace Yourself - 2001 includes: Patrick Cavanaugh as Charlie Kristen McCullough as Sarah
to be papered for what is coming