a party member from the "future" quickly approaches the party from the
direction they are proceeding.  S/He addresses her/his younger/past
self. 

"I only have a few seconds!  <pant> I thought we were farther ahead
than here, and of course i had to avoid the BLANK back there!  NAME, i
know this is difficult to believe right now, but i have to have my --
or your -- OBJECT right now. I am you, except two days into the
future!  Everything should be fine if you give it to me now... noone
is hurt yet, but we lost most of our possessions, but i can get them
back if you give me the OBJECT now.  I must leave.  You -- everyone,
must act as you will without my knowledge.  Everything should be
okay."

If there is any delay or any questions they will be trounced with
pleading by the character for swift decision.  Start a stop-watch when
you introduce the character.  Before introducing the character pay
attention to all names that are used and any personal info.  the
"future" character is really a doppledanger and will use any info if
available.  but note, s/he will not use it in answering questions,
s/he will simply info/name-drop to make it appear more convincing.
OBJECT will be something unique and difficult to replace (magic book,
magical non-weapon item, etc.) and reasonable to expect that it alone
would greatly aid in some forseeable circumstance.  note: the object
must be presumed or have been observed.  after one minute of real time
plead one final time, but then it must leave.  if it hasn't worked by
then, the doppledanger picked the wrong dupe.