In a similar situation I used a space battle between small fleets of un-
known alien ships.
The two fleets suddenly appeared out of "nowhere" (jump space, pro-
bably) and began to fire on each other with grasers and some kind of
unknown gravitic weapons, and the battle moved closer and closer to
the characters' ship.
Some near misses with gravitic weapons caused strange effects on the
characters' ship, and they received a number of completely unintelligi-
ble laser communication signals obviously directed at them.
The characters attempted to maneuver away from the battle, but the
alien ships were much fast than their ship, so they never really made
it to a more safe region, and the battle all around them became more
and more threatening (imagine being in the middle of a Star Wars batt-
le in a space shuttle ...).
Then suddenly a single ship of a third alien type "appeared" and began
to systematically destroy all ships of the other two species with another
unknown type of weapon.
The two fleets that had fought each other "disappeared" after heavy los-
ses, and the single alien ship drew close to the characters' ship and ob-
viously scanned it with some very powerful sensors (destroying some mi-
nor electronics in the process) - and then "disappeared", too.
Although the characters had not much to do except watch the scene and
hope to survive, the players really liked that "encounter".
