Trying to extract limitless amounts of energy from nuclear fusion has proved tantalisingly difficult. Scientists are still struggling with huge reactors capable of containing the temperatures and pressures needed to make nuclei fuse. But there is another way: persuading a particle called a muon to squeeze together adjacent nuclei. Muon-catalysed fusion has faced two big hurdles. Now an international team has cracked one of these, with a nifty way to bump up the number of nuclear reactions each muon achieves before it decays. Meanwhile, a group of Japanese physicists is making progress on the other.