Which TV show did “Simon & Simon” famously crossover with?

Television crossovers back then were usually just quick guest spots that wrapped up in a single episode, and half the time they didn't even count as real events in the show's history. But CBS knew that to turn around "Simon & Simon," they were going to need to pull off something brand new. CBS paired the struggling show with Tom Selleck's "Magnum, P.I." for television's first cliffhanger crossover between two different series. 

The network moved "Simon & Simon" to Thursday nights right after "Magnum," then launched the second season with a sneaky two-part story that started on the "Magnum" episode "Ki'is Don't Lie." When the villain escapes at the end of that episode, viewers had to stick around for "Simon & Simon" to see the conclusion in "Emeralds Are Not a Girl's Best Friend." CBS basically kidnapped Tom Selleck's massive audience and forced them to give the Simon brothers a chance. The plan worked immediately, turning "Simon & Simon" from a ratings disaster into a top ten hit for the next three seasons.