Aliens not included. Hopefully.
The plot is said to be based on one of the other books in the series.
"If Nazis are back, I'm back. But that's not necessarily the theme of the new Indiana Jones script. We're working on a script. And I'm looking forward to having the opportunity to work with Steven again, and revisit that character in a different story, at a different age." -Harrison Ford, 9/22/17
Hopefully they learned a lot from their previous movie, Kingdom of the Crystal Skull. Shia LaBeouf’s character isn’t set to return, and this will be the first Indiana Jones movie that doesn’t have George Lucas signed on as a writer. Spielberg is still involved, John Williams will be composing, and Harrison Ford will be reprising his role of Indy. So there are many positives to this already, though it is unclear if Short Round will be returning.