get to the bottom of

get to the bottom of: descobrir a real causa de algo, ir até o fundo de alguma coisa, saber a verdadeira história por trás de algo

“The police don't know who did the robbery yet, but they promised to get to the bottom of it. “(www.englishclub.com)

“I'm not sure how a mistake like this could happen, but I'm determined to get to the bottom of it and make sure it never happens again.”(www.englishclub.com)