Fluent Nhibernate inner join
Master
public virtual int Id { get; private set; }
public virtual Imagen imagen { get; set; }

Imagen
public virtual int Id { get; private set; }
public virtual Linea linea { get; set; }

Linea
public virtual int Id { get; private set; }
public virtual String Nombre { get; set; }

SELECT * FROM dbo.Master
INNER JOIN dbo.Imagen ON dbo.Master.imagen_id = dbo.Imagen.Id
INNER JOIN dbo.Linea ON dbo.Imagen.linea_id = dbo.Linea.Id
WHERE dbo.Linea_Id = 5

ICriteria c = session.CreateCriteria(typeof(Master))
  .CreateAlias("dbo.Imagen", "img", JoinType.InnerJoin)
  .Add(Restrictions.Eq("img.linea_id", id_linea));

return c.List<Master>();

var list = session.QueryOver<Master>()
                        .JoinQueryOver(master => master.imagen)
                        .Where(imagen => imagen.linea.Id == 5)
                        .List();

ICriteria c = session.CreateCriteria(typeof(Master))

.CreateAlias("imagen", "img", JoinType.InnerJoin)
.CreateAlias("img.linea", "lin", JoinType.InnerJoin)
.Add(Restrictions.Eq("lin.Id", 5));

return c.List<Master>();