Hm.

Sinistra — what were you thinking as means by which to send the message? I can think of several options, of varying levels of security, but you know him best.

I am concerned that Narcissa might accidentally give away that Auror Brodie has been her contact, should Dolohov go to her with his suspicion. With Dolohov so close to Crouch, that may be something he feels honour-bound to report.