The supermarket scandal sheets will go to amazing lengths to try to “out” even the straightest Hollywood stars, a new tell-all on the tabloid biz reveals.

That’s the assignment freelance writer Marlise Elizabeth Kast got when editors at Globe asked her to check out their bizarre suspicions that longtime friends Tobey Maguire, whose “Spider-Man 3,” opens Friday, and Leonardo DiCaprio, star of “Blood Diamond,” were lovers.

In “Tabloid Prodigy,” out this month from Running Press, Kast writes how she tracked ...