Pop superstar Whitney Houston is facing court action brought by her father's entertainment company for breach of contract. The suit alleges that the singer was facing financial difficulties and drug charges until her father's company intervened on her behalf. The company engaged an attorney to negotiate the dropping of the drug charges as well as a $100 million recording deal with Arista Records, said court documents. When the firm sought compensation for its services, it was refused.

If this action is based on agency law, what will Houston's father's entertainment company be obliged to prove?