Sienna Brooks

Sienna is on duty when Langdon wakes up with a head wound. Minutes later, the assassin Vayentha storms the hospital, shooting. Sienna gets Langdon out and hides him in her apartment, where the two find the projector showing Botticelli's Map of Hell.

She tells him he came in with a head wound and lost his memory of the past few days. For a man who lives on remembering symbols, dates and names, that's the worst problem there is. Sienna decides to stay by his side and help him piece it together.

With Sienna, Langdon follows Bertrand Zobrist's clues across Florence, reaches Dante's death mask and heads to Venice. She's with him every step and helps them dodge the men who claim to work for the WHO.

At the Palazzo Vecchio, the two slip through hidden passages and find that Dante's mask is gone. The culprit is Langdon himself, who hid it and can't remember doing so. Sienna proves quick at reading clues and finding exits, and the pair keeps going.

When Langdon works out that the target is the Hagia Sophia in Istanbul, Sienna leaves him. She was Zobrist's lover and wants to finish his plan. Sims, of the Consortium, tells Langdon that Sienna hired the firm and that the hospital was staged.

To Sienna, Zobrist was right: humanity is growing too fast and heading for collapse. She believes the virus is the only way out and uses Langdon's wiped memory to get to it.

In the Basilica Cistern, Sienna and Zobrist's followers try to burst the virus bag with an explosion. She kills Sims and ignores Langdon's pleas. The blast goes off, but Elizabeth Sinskey has already sealed the bag in a container, and Sienna doesn't make it out.

Langdon tries until the last second to convince her there's another way. She won't listen. The plan Sienna helped build ends up contained by the WHO, sealed off from the world outside. Langdon walks out of the cistern alive, alongside Sinskey, and heads back to Florence to tie up the trip's last loose end.

In the books, Sienna appears in Dan Brown's Inferno (2013). The film changes her path a lot at the end.