Who knows? According to Variety, Tom Hanks “has not yet committed to reprise the role” of Robert Langdon, “though he is expected to.” Will it hinge on Ron Howard’s involvement? Variety only states that Howard is on in a producer capacity. Definitely on board, however, is British screenwriter Steven Knight (EASTERN PROMISES) who will adapt the story which “finds [protagonist] Robert Langdon summoned to Washington, D.C., where he begins decoding the symbols of the Freemasons.”
Freemasonry is a fraternity with origins back in the late 16th century that have always remained rather unclear. They tend to be seen as a secret society and are the center of about a million different conspiracy theories. Do a Google search and see for yourself. Some of it is pretty interesting, most of it rather ridiculous.