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]
(..) Go on. Step up. Now hold on to the railing. - Keep your eyes closed. Don't peek. - l'm not. Step up onto the rail. Hold on... Hold on. Keep your eyes closed. Do you trust me ? l trust you. All right... (..)1997 Titanic