Inferno drastically underperforms at the box office.
The newest adaptation of a Dan Brown novel, Inferno, didn't even manage to take the #1 spot at the box office in its opening weekend (it lost to Boo! A Madea Halloween, in its second week). It took in a paltry ~$15 million, which is less than it was tracking to make - and more importantly a significant drop from its predecessors. Angels & Demons, the previous film in the franchise, opened to ~$46 million. The first film, The Da Vinci Code, opened at ~$77 million. If you're able to do basic math, you'll note that this is a $31 million drop with each subsequent film. At that pace, a fourth film would lose $16 million, something that is impossible, but nonetheless very funny (to me).
One has to assume that this puts the franchise in - at the very least - a bit of jeopardy. Most likely, though, this is the end of these movies. We've had diminishing returns in terms of profit and, as far as I'm concerned, that's been echoed in the quality of the films. Even with the international interest remaining somewhat strong, it seems very unlikely that a fourth movie ever gets made.
The Da Vinci Code was a flash-in-the-pan success, one that dominated conversations for a couple of years, but after it was over it was really over. It was a cultural phenomenon, but at this point in time isn't something that is often thought about.
The second movie did make money - especially from international markets - so perhaps it was worth at least attempting to turn a profit from the third one, but the experiment failed. We've moved on from Robert Langdon, and it's time for talented filmmakers like Ron Howard and Tom Hanks to put the character to rest.