[PHP] string error

This line is giving me an error.

$theSec = "$_GET['sec']" . ".php";
Parse error: parse error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRING or T_VARIABLE or T_NUM_STRING in /homepages/27/d115946677/htdocs/index.php on line 68

What does it mean? The whole snippet is:


	<?php
		//homepage code
		function secCode()
		{
			echo("homepage");
		}
	
		//default to homepage
		if(!$_GET['sec'])
		{
			$theSec = "index.php";
		}
		
		//choose the right section code
		else
		{
			$theSec = "$_GET['sec']" . ".php";
		}
		include($theSec);
		secCode();
	?>