Chasing Trouble

Chasing Trouble is a 1940 American comedy-drama film directed by Howard Bretherton, from Monogram Pictures.
Plot summary.
Frankie "Mr. Cupid" O’Brien (Frankie Darro) and Thomas H. Jefferson (Mantan Moreland) are making deliveries for the local florist and manage to get a job for their unemployed friend, Susie Carey (Marjorie Reynolds).
They are unaware that the proprietor, Mr. Morgan (Alex Callam), is part of a spy and saboteur ring which is using the florist shop as a front for delivering coded messages and bombs.
Using lesson two of his correspondence course on graphology, Frankie learns the truth but it might be too late for intrepid investigative reporter Callahan (Milburn Stone) and the police to help them before the bomb they are supposed to deliver goes off at an airplane factory.