The construction of the time machine started by Henry Branwell in 1865 has been completed. When Tessa Gray finds out about this ingenious invention started so many years ago by someone she'd grown to love, her biggest wish is to use it, to travel back in time and find out why she had Magnus Bane place a memory block over her mind like a veil. The only problem is, if she transfers back to the time when she was young, she'd only confuse herself and the people she loved. So instead of her travelling back into her past herself, she sends the only people she thinks worthy of the task: the new generation of shadowhunters. Clary, Jace, Isabelle and Alec...

When Tessa, Will and Magnus are transported from 19th century England to 21st Century New York things get a little complicated. Clockwork Princess and City of Heavenly Fire spoilers