When the crowd responded to the show so positively, we realized we were 'onto something'. [=we had done/discovered something important, special, etc.]
Scientists believe they are 'onto' something big. [=scientists believe they are close to making an important discovery]
Don't try to shift the blame 'onto' me. [=don't try to blame me instead of the person who should be blamed]
(..) And Lily Potter cast herself between them... ... the curse rebounded. When that happens, a part of Voldemort's soul... ... latched itself onto the only living thing it could find... ... Harry himself. There's a reason Harry can speak with snakes... There's a reason he can look into (..)2011 Harry Potter and the Deathly Hallows: Part 2