In the gym 6 can't jump on the seesaw - and 4 feels ill too - they've both got the dreaded lurgi. A boy can't stop bouncing up and down on a trampoline. 5 flies out to investigate, while 4 and 6 go for a lie down, leaving 3 in charge at base.
Other people, including the cook, have trouble with things going up and down or round and round. The Numberjacks try to send Brain Gain to get things sorted, and various agents give their help. 3 finally manages to send Brain Gain by falling on the Brain Gain button.