The clockwork angel was a pendant worn and owned by Tessa Gray and previously by her mother, Elizabeth. It had the soul of the angel Ithuriel trapped inside of it in order to protect Tessa from death.
The clockwork angel was made by John Shade as a gift to his wife Anne, but he never got a chance to finish it. His adopted son, Axel Mortmain, spent years finishing the pendant after his adoptive parents' death. He tuned it to the life of Tessa Gray, while she was still unborn, and gave it to her mother, Elizabeth, to make sure that Tessa would survive her birth and not become stillborn. The angel, since tuned to Tessa's life, was designed to save her from death, and thus, the delivery was a success and Tessa was born. Elizabeth continued to wear it for years after that and even had it with her when she died in the carriage accident.
After Elizabeth's death, Tessa's brother, Nate, found it in their mother's jewelry box and gave it to Tessa when he found that it still ticked, though there was no way to wind it. After that, Tessa has always worn it, rarely taking it off. She saw it as a symbol of her mother and her life in New York. Tessa brought it with her when she came to London.
When Mortmain attacked the London Institute, the angel grew blades and fought off his automatons. It disappeared for a while but returned to her days later. The angel again saved her life in Yorkshire when an automaton sent by Mortmain attacked them.
When Tessa, posing as Jessamine Lovelace, went to see Nate, she left the pendant behind. Before he died, Nate told her to keep the pendant close. When Tessa soon learned the truth about the pendant from Mortmain himself, she tried to destroy the pendant, only to summon Ithuriel. Tessa then used the angel pendant to Change into Ithuriel to defeat Mortmain, which also almost killed her in the process. This set Ithuriel free, and caused the angel pendant to stop ticking.
- Tessa had been trying to Change into her mother using the pendant, but it never worked.
- After Tessa slept with Will Herondale, the angel came into contact with his shoulder and left behind a star-shaped mark that soon became a birthmark every male Herondale was born with.