He's doing a huge amount of research this summer. He's not discussing it at all. He leaves all of his equipment and notes behind at whatever location he's working at. He's given me no hints what-so-ever about what or where. Often I can make some guesses based on what books he's looking at, but whatever project this is so secret he's keeping even his reading about it separate.

He's not happy when he gets back. Which worries me a fair bit. He's willing to happily discuss and work on a great many disturbing things. A list of stuff that bothers him is vanishingly small.