My code won't work

//Problem: User when clicking o immage goes to a dead end
//Solution: Create an overlay with the large image - Lightbox

var $overlay = $("<div id='overlay'></div>");
var $image = $("<img>");
var $caption = $("<p></p>");

// An image to overlay
$overlay.append($image);

 //Add overlay
$("body").append($overlay);

 // A caption
$overlay.append($caption);

// Capture the click event on a link to an image
$("a #imageGallery").click(function(event){
  event.preventDefault();
  var imageLocation = $(this).attr("href");
    // Update overlay with the image linked in the link
  $image.attr("src", imageLocation);

   // Show the overlay
  $overlay.show();
  // Get child's alt attribute and set caption
  var captionText = $(this).children("img").attr("alt");
  $caption.text(captionText);
});


// When overlay is clicked
$overlay.click(function(){
 // Hide the overlay
  $overlay.hide();
});