Ismark isn't a typically dour Barovian. He invites the
characters to join him, offers to pay for their wine, and
asks for their aid in protecting his adopted sister, Ireena Kolyana. If they agree to help, he takes them to the burgomaster's residence (area E4).

Escort Ireena

He wants the characters
to help him escort Ireena to Vallaki, a settlement in the
heart of the valley, beyond the view of Castle Raven loft
and (he hopes) beyond the reach of Strahd. Ismark
knows that moving Ireena is a gamble, since she's vulnerable to Strahd when she is outside their home, but he
has heard assertions that Vallaki is well defended.
Ismark has spent most of his adult life training with
weapons in the hope of one day confronting and killing
the Strahd. If the characters suggest that he accompany
them, Ismark agrees provided that Ireena is first taken
to a place of safety. As long as Ismark accompanies the
characters, he acts as a party member for the purpose of
determining each character's share of experience points
(though he gains no experience points himself).

What He knows

Ismark is as tight-lipped as any of the other Barovian
villagers, unless the talk deals with Ireena or Strahd.
Ismark knows everything the other villagers know. He
also knows that, for some unknown reason, Strahd is
attracted to Ireena and desires her above all others.

"Plea for Help"

If you used the "Plea for Help" adventure hook and
the characters show Ismark the letter they received, he
knows the burgomaster's handwriting well enough to
confirm that the letter was not written by his father.