What is the test for a cause of action for false imprisonment?

Passing upon a factual situation and contentions somewhat analogous to ours the court in Shakespeare v. City of Pasadena, 230 Cal.App.2d 375, 382, 40 Cal.Rptr. 863, 868, held that where a peace officer accepts delivery of a person following a citizen's arrest, 'By express statute, the officers under these circumstances are not liable for their actions (Pen.Code, 847) and, in fact, the officers would themselves have been criminally liable had they refused to take plaintiff into custody (Pen.Code, 142).' That case dealt with a cause of action for False arrest. A companion case, Shakespeare v. City of Pasadena, supra, 230 Cal.App.2d 387, 40 Cal.Rptr. 871, under similar factual circumstances found a contention of False imprisonment invalid, the court stating (p. 389, 40 Cal.Rptr. p. 872.): '* * * plaintiff here alleges not detention in connection with her arrest * * * other than that necessarily incident to the action of the police officers in carrying out their statutory duty to accept custody of one arrested by a citizen and hold such person for appearance before a magistrate. * * *'