Who is Mike Lundgren from The Madonnas of Leningrad: A Novel and what is their importance?

When, in the present day timeline, Marina goes missing, Mike Lundgren is the young fireman assigned to act as a liaison between the official search organization and Marina's family. Narration portrays him as quiet, compassionate, efficient and, for just a glimpsed moment, as a male figure that the recently divorced Helen might possibly feel some attraction to.