I'll take a stab. It comes in at 147 characters. It doesn't use strict, but does execute multiple times. 
sub decipher {
@n=split//,'_abcdefghijklmnopqrstuvwxyz.';$l{$n[$_]}=$_ for 0..$#n;@c=
+map{$l{$_}}split//,pop;$p[$_[0]*$_%@c]=$n[($c[$_]+$_)%@n]for 0..$#c;j
+oin'',@p
}

[download]

I was trying to find a way to not do the whole listing out of the 28 characters, but couldn't figure a way to get a-z into there. That could cut up to 23 characters, bringing me to 124.

Update: I've figured out a way to improve that string assignment. I feel stupid, but it's better now, down to 120. (Thanks, boo_radley!) 

@n=(_,a..z,'.');map{$l{$n[$_]}=$_}0..27;@c=map{$l{$_}}split//,pop;$p[$
+_[0]*$_%@c]=$n[($c[$_]+$_)%@n]for 0..$#c;join'',@p

[download]

------
/me wants to be the brightest bulb in the chandelier!

Vote paco for President!

In reply to Re: (Golf) Untwist by dragonchild
in thread (Golf) Untwist by ebbeatty

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