It was so damn simple, and he had never even thought of it. Carvalho was the man. Carvalho was shrewd and quiet, a man who could keep his intentions to himself and wreck an expedition without so much as being suspected. Subconsciously, Lamoureux hadn't quite believed in McCracken's guilt, despite the seeming evidence against him. McCracken had too genuine a love of horseplay, and of childish showing off.
These things were hard to pretend. You didn't put snow down somebody's back when you were plotting to leave him marooned on a deserted planet. And you didn't impress people by making a seventy-five foot broad jump when you could impress them much more effectively by condemning them to slow death.
Once he had thought of it, Lamoureux couldn't doubt. Carvalho had turned off the radio beam at the ship. By now the Astrolight was probably somewhere in space, possibly proceeding to some rendezvous with a rival expedition. Carvalho wouldn't dare appear back on Earth as the lone passenger returning on Lamoureux's ship. But he wouldn't have to. He could set the Astrolight adrift, be "rescued" by the people who had employed him, and come back to tell of the dangers he had braved on Mercury.
It all fitted in. Carvalho had been the one who had tried to hamper their work from the moment they had landed. When McCracken had shot that Mercurian—
Lamoureux asked, "What happened then? Try to remember."
McCracken scratched his head vigorously. "I think Carvalho saw this Mercurian and started to yell and run. I thought he was scared. That's why I shot."