Laconic / And Another Thing...

The Trope
Character mentions something important from the doorway, just as they are about to leave.

The Novel
The characters from Douglas Adams's The Hitchhiker's Guide to the Galaxy series are given another shot at life by the author of the Artemis Fowl books.
By the way, visit the unabridged version of the trope HERE. Oh, almost forgot, read about the novel HERE. Farewell.