The drums of jeopardy and Stefani Gregor and Johnny Two-Hawks, all interwoven.

She had waited in vain for Cutty to mention the emeralds.

What signified his silence?
She had indirectly apprised him of the fact that she knew the author of that advertisement offering to purchase the drums, no questions asked.

Who but Cutty in New York would know about them?
The mark of the thong.

Johnny Two-Hawks had been carrying the drums, and Karlov's men had torn them from their victim's neck during the battle.
Was there any reason why Cutty should not have taken her completely into his confidence?
Palaces looted.