This was implied by a few things at the end of season four, including Sierra’s disobeyal of police instructions when speaking about Rio’s (Miguel Herran) torture.
As well as this, in the final credits, Nimri is the person singing the latest version of Bella Ciao, which might be an indication she is joining the rebellion.
While another fan named StudentDoctor1908 theorised on Reddit: “Sierra will definitely be a front and centre antagonist next season, second only to the police.
“It’s obvious that now that she has the Professor, they’ll have to see what she does next and how the gang deals with her.”
Viewers will just have to wait and see what happens when the show finally returns to Netflix.
Money Heist seasons 1-4 are currently available to stream on Netflix.