Simplify the following text for a Grade 10 native English-speaking person.
Original: In the episode , Bart catches a glimpse of the original issue of Radioactive Man for sale at a comic book convention , so he , Martin , and Milhouse combine their money to buy the valuable comic book , only to lose it due to their selfishness and inability to share .
Simplified: In this episode , Bart catches a quick look of the ( ( wikt : original original issue of `` Radioactive Man '' for sale at a comic book convention . So Bart , Martin , and Milhouse combine their money to buy the valuable comic book , only to lose it because to their selfishness and being unable to share .