Whipsaw is the picture that answers that burning question in the title.
This was Spencer Tracy's second film under his new MGM contract when he switched studios from Fox in 1935. With few exceptions Tracy starred in routine action films while at Fox and working in Whipsaw must have made Spence feel he was still at Fox. Other than the fact Louis B. Mayer instead of Darryl Zanuck was signing his paycheck, he wouldn't have known the difference from the quality of material he was being asked to do.
Myrna Loy however had already found her screen persona in The Thin Man a year earlier at MGM. So why she was asked to do Whipsaw is beyond me.
Basically the plot is Myrna is the confederate of jewel thief Harvey Stephens who's just made a big score. Stephens has a problem though, he's got to watch out for the law and for another gang who wanted in on the robbery.
The FBI has decided that the best way to Stephens is through Myrna and they've sent ace G-Man Spencer Tracy to work undercover and gain her confidence. Of course Spence gains more than her confidence.
So how will it work out for our intrepid duo? See the film if you are big fan of both of the stars, but only if that. Myrna and Spence both did much better work.
But big things were breaking for Tracy soon. He got cast as Father Timothy Mullin in San Francisco, got the first of his Oscar nominations, changed his screen image, and the rest as he later said in one of his better films is cherce.
As for Loy, I'm sure she was grateful to get back to working with William Powell in another Thin Man film. In fact she got to work with Powell and Tracy in Libelled Lady one of the best screen comedies from MGM ever. See that film by all means.
