In 1876 Boston, Aleck (Alexander Graham Bell) is a teacher of the deaf who has been hired to tutor Mabel Hubbard, the deaf daughter of a wealthy businessman, Gardiner Hubbard and his wife Gertrude. Aleck and Gardiner quickly discover that they have a mutual interest in scientific invention.

1 – Invention (ALECK, GARDINER)

Mabel explains to Aleck exactly what she expects from her lessons. (Mabel only sings when she is alone with Aleck, because only Aleck can hear her sing.)

2 – Different (MABEL)

Gardiner, a patent attorney who needs to replenish his bank account, wants Aleck to work on developing a multiple telegraph – a telegraph that can transmit several messages on one wire. Aleck feels that invention is a sideline, that his real calling is as a teacher of the deaf.

3 – You Were Called (GARDINER)

Mabel has attended one of the public lectures Aleck gives about his father’s phonetic writing system, and is most impressed by how Aleck is transformed from a shy teacher into an authoritative speaker when he is in front of a crowd.

4 – The Orator (ALECK)

Gertrude is worried about the family finances, but Gardiner tells her everything will be all right – they’re “the right sort of people”.

5 – The Right Sort of People (GERTRUDE)

Aleck explains his father’s “Visible Speech” system to Mabel.

6 – “Serious Fun” (MABEL, ALECK)

Aleck wants to court Mabel, but realizes that her parents, especially her father, may be an obstacle.

7 – “May I Tell Her?” (ALECK)

Aleck wants to pursue his “acoustic telegraph” idea rather than the multiple telegraph, and Mabel decides to help him persuade her father to support the plan.

8 – “Everybody’s Face” (MABEL)

Gardiner is bothered by the growing relationship of his daughter and the young inventor, but Gertrude reminds him that he was once a young suitor, too.

9 – “Perhaps” (GERTRUDE, GARDINER)

Finally Aleck is allowed to court Mabel, but the young lovers agree not to make definite plans. They vow to let things remain “up in the air”.

10 – “Up in the Air” (MABEL, ALECK)

Gardiner has been asking about other inventors and other attempts to patent an acoustic telegraph. He has made plans for Aleck to go to Washington DC, to see certain people and look at certain documents. Aleck wants to stay in Boston to be with Mabel. Gardiner explains his theories about “love”.

11 – “Love” (GARDINER)

Finally Aleck has successfully created an acoustic telegraph, which Gardiner has already patented and which he hopes will earn everyone a fortune. Aleck is uncomfortable, however, and wants to be rid of the project.

12 – “The Orator (reprise)” (ALECK)

Aleck rehearses how he will confess to Mabel that when in Washington DC he saw Elisha Gray’s patent application, which gave him the right idea to complete his own acoustic telegraph. He feels guilty to have “stolen” the idea. But before he can come clean with Mabel, she – already suspecting something – forestalls his attempts to admit guilt.

13 – “Your Wife” (MABEL)