Justice League Unlimited #20,
VERY FINE/NEAR MINT
Written by Paul Storrie, art by Rick Burchett, cover by Ty Templeton.
Mary Marvel is feeling a little overwhelmed at the Justice League Watchtower, so Supergirl decides to take her out to watch an actual League mission. But when that mission goes bad, and Wonder Woman's strike team finds itself on the verge of defeat, does Mary have what it takes to step up and save the day?