I use that spoiler on my board too.

I like it much more than the other ones around. Here's what you want to use...
Title:
Spoiler Block
BB Code Tag Name:
spoiler
Replacement:
Code:
<div style="margin: 5px;">
<div class="smallfont" style="margin-bottom: 2px;">
<b>Spoiler!</b> <input value="Show" style="margin: 0px; padding: 0px; width: 45px; font-size: 10px;" onclick="if(this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display != 'inline')
{ this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display = 'inline'; this.innerText = ''; this.value = 'Hide'; }
else
{ this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display = 'none'; this.innerText = ''; this.value='Show'; }" type="button">
</div>
<div class="alt2" style="border: 1px inset; padding: 6px;">
<div class="spoiler" style="display: none;">{param}</div>
</div>
</div>
You can change the blue Spoiler! in the above code to anything you want, like "Official Plot Synopsis"
Example:
[spoiler]HIDE ME![/spoiler]
Description:
This will add a spoiler block to require users to click so that they cannot immediately view what has been posted.
Use {option}:
No
Remove Tag If Empty:
Yes
Disable BB Code Within This BB Code:
No
Disable Smilies Within This BB Code:
No
Disable Word Wrapping Within This BB Code:
No