While visiting the Summer Court, Feyre briefly saw the necklace in Tarquin's trove.
After Feyre stole half of the Book of Breathings from the Summer Court, Tarquin sent three blood rubies to the Court of Nightmares, declaring that they were enemies of his court. After hearing news of this, Varian sent Amren a necklace of diamonds and rubies to soften the declaration of the blood feud. The necklace was placed beside her bed, as if she fell asleep looking at it.
Despite the connotations of the necklace Amren took to wearing it at all times. After Tarquin rescinded the blood rubies due to the Night Court aiding his court against Hybern, Cassian remarked that he shouldn't expect Amren to return the necklace as she had grown attached to it.