Aura of Determination

There seems to be a bit of confusion regarding the wording on this trait around our gaming table. Does it act as a call-on only for “great effort” tests that involve multiple characters, or can it be used by any single character in the possessing character’s presence? I.e., if Fred the Dwarf has this trait and is with Sasha the Sorcerer and Bubba the Elf in a scene, when Fred fails a persuasion test with an NPC can he use his Aura of Determination, or does it only work if Sasha and Bubba are both helping him with the test?

We’ve interpreted as tests involving multiple characters.